Business Combinations - Results of Operations (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	$ 5,696		$ 7,422
Business Combination Pro Forma Information Income Loss Before Income Taxes Of Acquiree Since Acquisition Date Actual	552		846
Total revenues	422,543	$ 407,222	834,285	$ 779,257
Income before income taxes	102,009	104,775	198,277	194,274
Net income	$ 61,667	$ 63,572	$ 120,128	$ 117,594
Net income per share:
Basic (in dollars per share)	$ 0.44	$ 0.44	$ 0.85	$ 0.81
Diluted (in dollars per share)	$ 0.43	$ 0.43	$ 0.83	$ 0.80
Weighted Average Basic Shares Outstanding, Pro Forma	137,518	141,250	138,434	141,428
Weighted average number of shares outstanding:
Pro Forma Weighted Average Shares Outstanding, Diluted	139,828	143,032	140,647	143,169