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Stock-Based Compensation - Performance Based Units Earned under Long-Term Incentive Plan (Detail) - Performance Stock Units [Member]
12 Months Ended
Dec. 31, 2015
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Number of Units Outstanding, Beginning Balance, Nonvested | shares 83,515
Number of Units, Earned | shares 231,543
Number of Units, Vested | shares (111,448)
Number of Units, Canceled | shares (13,144)
Number of Units, Accrued dividend equivalents | shares 1,070
Number of Units Outstanding, Ending Balance, Nonvested | shares 191,536
Weighted Average Grant-Date Fair Value, Nonvested, Beginning Balance | $ / shares $ 24.11
Weighted Average Grant-Date Fair Value, Earned | $ / shares 36.62
Weighted Average Grant-Date Fair Value, Vested | $ / shares 32.12
Weighted Average Grant-Date Fair Value, Canceled | $ / shares 31.22
Weighted Average Grant-Date Fair Value, Accrued dividend equivalents | $ / shares 24.18
Weighted Average Grant-Date Fair Value, Nonvested, Ending Balance | $ / shares $ 34.18