Schedule of Selected Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information [Line Items]
Revenue	$ 464,134	$ 474,935	$ 463,331	$ 447,385	$ 447,835	$ 459,957	$ 459,295	$ 426,000	$ 1,849,785	$ 1,793,087	$ 1,646,867
Operating income	80,359	73,953	77,176	64,928	66,539	65,436	79,753	68,826	296,416	280,554	240,296
Net income	$ 60,689	$ 55,340	$ 57,583	$ 46,307	$ 48,598	$ 50,676	$ 65,303	$ 57,277	$ 219,919	$ 221,854	$ 195,022
Basic earnings per share: Net income	$ 0.52	$ 0.47	$ 0.49	$ 0.39	$ 0.41	$ 0.43	$ 0.56	$ 0.49	$ 1.87	$ 1.90	$ 1.68
Diluted earnings per share: Net income	$ 0.52	$ 0.47	$ 0.49	$ 0.39	$ 0.41	$ 0.43	$ 0.55	$ 0.49	$ 1.87	$ 1.88	$ 1.66