Annual report pursuant to Section 13 and 15(d)

Financial Instruments - Composition of Financial Instruments (Detail)

v2.4.1.9
Financial Instruments - Composition of Financial Instruments (Detail) (USD $)
Dec. 31, 2014
Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 60,555,000us-gaap_AvailableForSaleSecuritiesAmortizedCost $ 60,293,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
Gross unrealized gains 8,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax 27,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Gross unrealized losses (50,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax (9,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Fair Value 60,513,000us-gaap_AvailableForSaleSecurities 60,311,000us-gaap_AvailableForSaleSecurities
Cash and cash equivalents [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,858,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_CashAndCashEquivalentsMember 		406,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_CashAndCashEquivalentsMember
Gross unrealized gains 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_CashAndCashEquivalentsMember 		0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_CashAndCashEquivalentsMember
Gross unrealized losses 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_CashAndCashEquivalentsMember 		0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_CashAndCashEquivalentsMember
Fair Value 1,858,000us-gaap_AvailableForSaleSecurities
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_CashAndCashEquivalentsMember 		406,000us-gaap_AvailableForSaleSecurities
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_CashAndCashEquivalentsMember
Investments [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 58,697,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_InvestmentsMember 		59,887,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_InvestmentsMember
Gross unrealized gains 8,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_InvestmentsMember 		27,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_InvestmentsMember
Gross unrealized losses (50,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_InvestmentsMember 		(9,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_InvestmentsMember
Fair Value 58,655,000us-gaap_AvailableForSaleSecurities
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_InvestmentsMember 		59,905,000us-gaap_AvailableForSaleSecurities
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_InvestmentsMember
US Government Agencies Debt Securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 27,154,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember 		26,532,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Gross unrealized gains 5,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember 		10,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Gross unrealized losses (8,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember 		(5,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Fair Value 27,151,000us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember 		26,537,000us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Corporate debt securities [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 31,543,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember 		33,355,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Gross unrealized gains 3,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember 		17,000us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Gross unrealized losses (42,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember 		(4,000)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Fair Value 31,504,000us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember 		33,368,000us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember
Money market funds [Member]    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,858,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember 		406,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember
Gross unrealized gains 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember 		0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember
Gross unrealized losses 0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember 		0us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember
Fair Value $ 1,858,000us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember 		$ 406,000us-gaap_AvailableForSaleSecurities
/ us-gaap_InvestmentTypeAxis
= us-gaap_MoneyMarketFundsMember