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Stock-Based Compensation - Deferred Stock Unit, Performance-Based Stock Unit and Restricted Stock Activity (Detail) - Deferred stock units, performance-based stock units and restricted stock [Member] - $ / shares
shares in Thousands
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Unvested, shares    
Unvested, Beginning Balance 455 317
Granted 286 231
Vested (64) (78)
Forfeited (7) (15)
Unvested, Ending Balance 670 455
Weighted Average Grant Date Fair Value    
Unvested, Beginning Balance $ 17.09 $ 15.34
Granted 15.02 19.67
Vested 17.42 17.91
Forfeited 18.76 15.61
Unvested ,Ending Balance $ 16.16 $ 17.09