Quarterly report pursuant to Section 13 or 15(d)

Financial Instruments - Composition of Financial Instruments (Detail)

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Financial Instruments - Composition of Financial Instruments (Detail) (USD $)
Mar. 31, 2014
Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 60,264,000 $ 60,293,000
Available-for-sale Securities Gross Unrealized Gain Accumulated in Investments 28,000 27,000
Available-for-sale Securities Gross Unrealized Loss Accumulated in Investments 11,000 9,000
Fair Value 60,281,000 60,311,000
Cash and cash equivalents [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 84,000 406,000
Available-for-sale Securities Gross Unrealized Gain Accumulated in Investments 0 0
Available-for-sale Securities Gross Unrealized Loss Accumulated in Investments 0 0
Fair Value 84,000 406,000
Investments [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 60,180,000 59,887,000
Available-for-sale Securities Gross Unrealized Gain Accumulated in Investments 28,000 27,000
Available-for-sale Securities Gross Unrealized Loss Accumulated in Investments 11,000 9,000
Fair Value 60,197,000 59,905,000
US Government Agencies Debt Securities [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 23,494,000 26,532,000
Available-for-sale Securities Gross Unrealized Gain Accumulated in Investments 9,000 10,000
Available-for-sale Securities Gross Unrealized Loss Accumulated in Investments 4,000 5,000
Fair Value 23,499,000 26,537,000
Corporate debt securities [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 36,686,000 33,355,000
Available-for-sale Securities Gross Unrealized Gain Accumulated in Investments 19,000 17,000
Available-for-sale Securities Gross Unrealized Loss Accumulated in Investments 7,000 4,000
Fair Value 36,698,000 33,368,000
Money market funds [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 84,000 406,000
Available-for-sale Securities Gross Unrealized Gain Accumulated in Investments 0 0
Available-for-sale Securities Gross Unrealized Loss Accumulated in Investments 0 0
Fair Value $ 84,000 $ 406,000