Business Combinations - Results of Operations (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Document Period End Date			Jun. 30, 2018
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual			$ 7,900
Business Combination Pro Forma Information Income Loss Before Income Taxes Of Acquiree Since Acquisition Date Actual			1,000
Total revenues	$ 478,414	$ 479,225	991,188	$ 956,510
Income before income taxes	102,056	111,018	223,189	224,855
Net income	$ 74,761	$ 67,948	$ 167,633	$ 139,874
Net income per share:
Basic (in dollars per share)	$ 0.27	$ 0.25	$ 0.61	$ 0.50
Diluted (in dollars per share)	$ 0.27	$ 0.24	$ 0.60	$ 0.49
Weighted Average Basic Shares Outstanding, Pro Forma	270,081	273,384	270,126	273,436
Weighted average number of shares outstanding:
Pro Forma Weighted Average Shares Outstanding, Diluted	275,908	278,202	275,809	278,128