Earnings Per Share - Summary of Earnings Per Share, Basic and Diluted (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income	$ 52,830	$ 116,770	$ 98,678	$ 94,153	$ 109,540	$ 95,509	$ 88,549	$ 75,109	$ 362,431	$ 368,707	$ 284,501
Denominator for basic earnings per share	92,321	92,110	91,904	91,750	87,877	83,611	82,996	82,737	92,023	84,317	81,793
Dilutive securities									2,116	2,665	2,862
Denominator for diluted earnings per share	94,350	94,157	94,050	93,934	90,240	86,134	85,817	85,695	94,139	86,982	84,655
Basic earnings per share	$ 0.57	$ 1.27	$ 1.07	$ 1.03	$ 1.25	$ 1.14	$ 1.07	$ 0.91	$ 3.94	$ 4.37	$ 3.48
Diluted earnings per share	$ 0.56	$ 1.24	$ 1.05	$ 1.00	$ 1.21	$ 1.11	$ 1.03	$ 0.88	$ 3.85	$ 4.24	$ 3.36