Summarizes Stock Appreciation Rights (SARs) Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options outstanding, beginning balance, shares	1,943,176	2,129,929	2,163,825
Granted, shares	605,000	510,000	160,000
Exercised, shares	(731,142)	(672,753)	(176,896)
Forfeited, shares	(132,500)	(24,000)	(17,000)
Stock options outstanding, ending balance, shares	1,684,534	1,943,176	2,129,929
Exercisable, Ending Balance	632,034	1,055,176	1,520,720
Stock options outstanding, beginning balance, weighted average exercise price	$ 12.19	$ 8.82	$ 8.12
Granted, weighted average exercise price	$ 30.15	$ 19.64	$ 12.88
Exercised, weighted average exercise price	$ 9.84	$ 7.21	$ 4.46
Forfeited, weighted average exercise price	$ 19.30	$ 11.27	$ 4.05
Stock options outstanding, ending balance, weighted average exercise price	$ 19.11	$ 12.19	$ 8.82
Exercisable, Weighted Average Exercise Price	$ 10.13	$ 12.21	$ 7.57
Stock options outstanding, weighted-average remaining contractual term	5 years 1 month 6 days	5 years 3 months 22 days	6 years 11 months 27 days
Exercisable, weighted-average remaining contractual term	3 years 11 months 19 days	4 years 6 months 29 days	6 years 2 months 12 days
Outstanding, aggregate intrinsic value	$ 30,111	$ 28,379	$ 5,640
Exercisable, aggregate intrinsic value	16,744	19,314	5,966
Stock Appreciation Rights (SARs)
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options outstanding, beginning balance, shares	495,000
Granted, shares	754,000	495,000
Exercised, shares	(68,750)
Forfeited, shares	(120,000)
Stock options outstanding, ending balance, shares	1,060,250	495,000
Exercisable, Ending Balance	35,000
Stock options outstanding, beginning balance, weighted average exercise price	$ 19.19
Granted, weighted average exercise price	$ 34.70	$ 19.19
Exercised, weighted average exercise price	$ 19.10
Forfeited, weighted average exercise price	$ 21.46
Stock options outstanding, ending balance, weighted average exercise price	$ 29.97	$ 19.19
Exercisable, Weighted Average Exercise Price	$ 19.43
Stock options outstanding, weighted-average remaining contractual term	6 years 1 month 10 days	6 years 6 months
Exercisable, weighted-average remaining contractual term	5 years 6 months 11 days
Outstanding, aggregate intrinsic value	9,991	3,770
Exercisable, aggregate intrinsic value	$ 602