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Share-based Compensation - Additional Information (Detail) (USD $)
3 Months Ended 0 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Share-based compensation expense recognized $ 1,777,000us-gaap_AllocatedShareBasedCompensationExpense $ 1,187,000us-gaap_AllocatedShareBasedCompensationExpense  
Shares issued under stock purchase plan 153,367us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans 263,575us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans  
Restricted Stock [Member]      
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Share-based compensation expense recognized     $ 0us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember