Earnings Per Share - Summary of Earnings Per Share, Basic and Diluted (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income	$ 129,618	$ 116,253	$ 111,090	$ 116,770	$ 227,343	$ 356,961	$ 309,601
Denominator for basic earnings per share (in shares)	92,631	92,665	92,516	92,110	92,591	92,604	91,923
Dilutive securities (in shares)	2,676			2,047		2,600	2,146
Denominator for diluted earnings per share (in shares)	95,307	95,279	95,030	94,157	95,137	95,204	94,069
Basic earnings per share (in dollars per share)	$ 1.40	$ 1.25	$ 1.20	$ 1.27	$ 2.46	$ 3.85	$ 3.37
Diluted earnings per share (in dollars per share)	$ 1.36	$ 1.22	$ 1.17	$ 1.24	$ 2.39	$ 3.75	$ 3.29