Quarterly Results of Operations (Unaudited) - Schedule of Quarterly Results of Operations (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 254,819	$ 241,750	$ 230,315	$ 204,073	$ 232,462	$ 224,724	$ 222,031	$ 193,155	$ 930,957	$ 872,372	$ 733,031
Cost of sales	142,497	135,250	124,993	110,787	132,244	132,131	133,203	116,328	513,527	513,906	451,666
Gross profit	112,322	106,500	105,322	93,286	100,218	92,593	88,828	76,827
Operating income	78,235	72,992	68,954	58,567	63,168	51,985	56,215	52,177	278,748	223,545	161,692
Net income	$ 59,087	$ 55,683	$ 51,324	$ 42,618	$ 47,063	$ 39,995	$ 42,927	$ 39,842	$ 208,712	$ 169,827	$ 119,209
Basic	$ 1.51	$ 1.41	$ 1.27	$ 1.05	$ 1.16	$ 0.98	$ 1.06	$ 0.98	$ 5.22	$ 4.18	$ 2.96
Diluted	$ 1.50	$ 1.40	$ 1.27	$ 1.04	$ 1.15	$ 0.98	$ 1.05	$ 0.98	$ 5.19	$ 4.16	$ 2.94