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Share Repurchases - Additional Information (Detail) (USD $)
8 Months Ended 12 Months Ended
Dec. 31, 2014
Dec. 31, 2014
Dec. 31, 2012
May 01, 2014
Equity [Abstract]        
Authorized a share repurchase under a stock repurchase plan $ 50,000,000us-gaap_StockRepurchaseProgramAuthorizedAmount1 $ 50,000,000us-gaap_StockRepurchaseProgramAuthorizedAmount1   $ 25,000,000us-gaap_StockRepurchaseProgramAuthorizedAmount1
Share repurchase program expiration date   May 01, 2016    
Repurchases, shares 755,310us-gaap_StockRepurchasedDuringPeriodShares 464,190us-gaap_StockRepurchasedDuringPeriodShares 374,000us-gaap_StockRepurchasedDuringPeriodShares  
Repurchases, amount $ 16,627,000us-gaap_StockRepurchasedDuringPeriodValue $ 12,200,000us-gaap_StockRepurchasedDuringPeriodValue