Selected Quarterly Financial Data (Unaudited) - Schedule of Selected Quarterly Financial Data (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, net	$ 376,697	$ 295,283	$ 273,502	$ 253,908	$ 255,501	$ 225,150	$ 220,869	$ 193,651	$ 1,199,390	$ 895,171	$ 707,534
Operating income	172,622	144,207	134,484	114,136	106,050	111,255	109,074	94,253	565,449	420,632	324,928
Net income	$ 109,540	$ 95,509	$ 88,549	$ 75,109	$ 68,120	$ 78,620	$ 73,099	$ 64,662	$ 368,707	$ 284,501	$ 216,199
Earnings per share:
Basic earnings per share	$ 1.25	$ 1.14	$ 1.07	$ 0.91	$ 0.83	$ 0.96	$ 0.90	$ 0.80	$ 4.37	$ 3.48	$ 2.59
Diluted earnings per share	$ 1.21	$ 1.11	$ 1.03	$ 0.88	$ 0.80	$ 0.93	$ 0.87	$ 0.77	$ 4.24	$ 3.36	$ 2.52
Weighted average shares outstanding:
Basic weighted average shares outstanding	87,877	83,611	82,996	82,737	82,388	81,974	81,573	81,222	84,317	81,793	83,328
Diluted weighted average shares outstanding	90,240	86,134	85,817	85,695	85,277	84,905	84,461	83,960	86,982	84,655	85,736