Stock-Based Compensation - SAR Activity (Detail) (Stock Appreciation Rights [Member], USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock Appreciation Rights [Member]
Schedule Of Stock Appreciation Rights Activity [Line Items]
SARs Outstanding, Beginning Balance	739,194	1,374,380	2,325,410
Granted, SARs	3,866	121,176	201,828
Exercised, SARs	(218,826)	(749,334)	(1,135,906)
Canceled, SARs	(8,404)	(7,028)	(16,952)
Shares Outstanding, SARs, Ending Balance	515,830	739,194	1,374,380
Outstanding, Weighted Average Grant Price Per Share, Beginning Balance	$ 12.93	$ 9.28	$ 6.59
Vested, SARs	383,488
Granted, Weighted Average Grant Price Per Share	$ 37.88	$ 21.95	$ 12.88
Exercisable, SARs	383,488
Exercised, Weighted Average Grant Price Per Share	$ 10.96	$ 7.70	$ 6.54
Canceled, Weighted Average Grant Price Per Share	$ 4.74	$ 13.10	$ 12.08
Outstanding, Weighted Average Grant Price Per Share, Ending Balance	$ 13.98	$ 12.93	$ 9.28
Vested, Weighted Average Grant Price Per Share	$ 12.55
Exercisable, Weighted Average Grant Price Per Share	$ 12.55
Weighted Average Remaining Contractual Life, Outstanding	6 years 6 months
Weighted Average Remaining Contractual Life, Vested	6 years 1 month 6 days
Weighted Average Remaining Contractual Life, Exercisable	6 years 1 month 6 days
Aggregate Intrinsic Value, Outstanding	$ 14,754,320
Aggregate Intrinsic Value, Vested	11,514,749
Aggregate Intrinsic Value, Exercisable	$ 11,514,749