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Stock Based Compensation - Additional Information (Detail) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Stock options granted, exercisable life 5 years    
Stock options remainder vesting period 3 years    
Stock options, authorized 4,657,552us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant    
Non-cash compensation expense $ 3,322,000us-gaap_ShareBasedCompensation $ 3,005,000us-gaap_ShareBasedCompensation $ 2,406,000us-gaap_ShareBasedCompensation
Tax benefits related to stock based compensation 0us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense    
Unrecognized compensation costs 2,800,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized    
Compensation costs expected to be recognized 2 years 6 months    
Cash proceeds from stock options exercised $ 5,700,000us-gaap_ProceedsFromStockOptionsExercised $ 3,700,000us-gaap_ProceedsFromStockOptionsExercised $ 3,300,000us-gaap_ProceedsFromStockOptionsExercised
Minimum      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Stock options vested period 3 years    
Maximum      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Stock options vested period 5 years