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Stock-Based Compensation - Summarizes Information of Performance Share Awards (Detail)
12 Months Ended
Dec. 31, 2015
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Non-vested at December 31, 2014 | shares 595,700
Granted | shares 163,400
Vested | shares (268,390)
Forfeited | shares (47,610)
Non-vested at December 31, 2015 | shares 443,100
Non-vested at December 31, 2014 | $ / shares $ 30.06
Granted | $ / shares 47.52
Vested | $ / shares 19.47
Forfeited | $ / shares 37.10
Non-vested at December 31, 2015 | $ / shares $ 42.15