Share-Based Compensation - Schedule of Restricted Stock and RSU Grants and Changes (Detail) (Restricted Stock and RSUs [Member], USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted Stock and RSUs [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Beginning Balance, Shares outstanding	1,041,189	1,297,906	1,002,125
Granted, Shares	429,759	348,264	707,249
Vested, Shares	(237,739)	(323,159)	(324,345)
Cancelled, Shares	(143,835)	(281,822)	(87,123)
Ending Balance, Shares outstanding	1,089,374	1,041,189	1,297,906
Shares outstanding - Weighted Average Grant Date Fair Value	$ 31.24	$ 28.61	$ 26.42
Granted, Weighted Average Grant Date Fair Value	$ 40.52	$ 38.28	$ 27.84
Vested, Weighted Average Grant Date Fair Value	$ 41.59	$ 37.02	$ 22.00
Cancelled, Weighted Average Grant Date Fair Value	$ 34.04	$ 30.04	$ 28.16
Shares outstanding - Weighted Average Grant Date Fair Value	$ 31.23	$ 31.24	$ 28.61