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Stock-Based Compensation - Schedule of Information Related to Outstanding SOSARS (Detail) - Stock Only Stock Appreciation Rights (SOSARs) [Member] - USD ($)
$ / shares in Units, $ in Thousands
 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Beginning Balance, Outstanding 1,864,707 1,977,133
Granted 406,142 275,529
Exercised (58,343) (19,199)
Canceled / forfeited (3,349) (24,719)
Ending Balance, Outstanding 2,209,157 2,208,744
Beginning Balance, Weighted Average Exercise Price, Outstanding $ 16.20 $ 13.91
Weighted Average Exercise Price, Granted 24.94 29.89
Weighted Average Exercise Price, Exercised 13.52 15.57
Weighted Average Exercise Price, Canceled / forfeited 26.53 18.85
Ending Balance, Weighted Average Exercise Price, Outstanding 17.87 15.83
Weighted average grant date fair value per share $ 7.54 $ 9.85
Aggregate grant date fair value $ 3,063 $ 2,713
Black-Scholes assumptions    
Dividend yield 1.92% 1.47%
Risk free rate of return 1.64% 1.73%
Volatility 36.48% 37.59%
Expected life 6 years 6 years