Business Combinations - Results of Operations (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	$ 9,218		$ 16,640
Business Combination Pro Forma Information Income Loss Before Income Taxes Of Acquiree Since Acquisition Date Actual	397		1,243
Total revenues	432,276	$ 431,703	1,267,812	$ 1,212,241
Income before income taxes	112,855	115,712	311,429	310,302
Net income	$ 67,442	$ 70,166	$ 187,738	$ 187,952
Net income per share:
Basic (in dollars per share)	$ 0.48	$ 0.49	$ 1.33	$ 1.30
Diluted (in dollars per share)	$ 0.47	$ 0.48	$ 1.31	$ 1.28
Weighted Average Basic Shares Outstanding, Pro Forma	137,684	140,915	138,181	141,253
Weighted average number of shares outstanding:
Pro Forma Weighted Average Shares Outstanding, Diluted	140,041	142,964	140,446	143,102