Summarizes Stock Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
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
Stock options exercisable, shares	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
Stock options outstanding, aggregate intrinsic value	$ 30,111	$ 28,379	$ 5,640
Exercisable, aggregate intrinsic value	$ 16,744	$ 19,314	$ 5,966