Annual report pursuant to Section 13 and 15(d)

Income Taxes - Additional Information (Detail)

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Income Taxes - Additional Information (Detail) (USD $)
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Income Tax [Line Items]        
Share-based compensation $ 9,984,000 $ 7,368,000 $ 4,215,000  
Federal tax credit carryforwards expiration date 2024      
Federal alternative minimum tax credit carryforwards 200,000      
Cumulative change in ownership 50.00%      
Period of cumulative change in ownership 3 years      
Valuation allowance on net federal deferred tax assets   6,700,000    
Unrecognized tax benefits 3,800,000      
Recognized tax benefits 3,100,000      
Accrued interest and penalties 0      
Period of change of unrecognized tax benefits 12 months      
Total unrecognized tax benefits 3,750,000 3,020,000 1,184,000 872,000
Benefits from tax holiday, tax rate 15.00%      
Statutory tax rate 25.00%      
Federal tax [Member]
        
Income Tax [Line Items]        
Net operating loss carryforwards 24,600,000      
Net operating loss carryforwards, expiration 2026      
Share-based compensation 6,400,000      
Tax credit carryforwards 5,200,000      
State tax [Member]
        
Income Tax [Line Items]        
Net operating loss carryforwards 26,700,000      
Net operating loss carryforwards, expiration 2018      
Share-based compensation 3,800,000      
Tax credit carryforwards $ 6,800,000