Quarterly Financial Information (Unaudited) - Quarterly Financial Data (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 Disclosure [Abstract]
Revenues	$ 319,775	$ 271,720	$ 296,215	$ 261,497	$ 312,120	$ 252,820	$ 274,036	$ 253,148	$ 1,149,207	$ 1,092,124	$ 1,040,991
Depreciation and amortization	27,928	26,706	26,409	28,773	28,916	28,498	28,399	28,570	109,816	114,383	112,278
Operating income	61,499	46,567	66,945	38,794	36,389	32,768	57,015	35,890	213,805	162,062	153,105
Income before income taxes	49,144	35,415	52,746	25,461	30,469	22,079	42,255	4,853	162,766	99,656	124,985
(Provision) benefit for income taxes	(1,048)	(1,822)	(1,415)	885	8,430	4,612	(866)	(321)	(3,400)	11,855	1,467
Net income	48,096	33,593	51,331	26,346	38,899	26,691	41,389	4,532	159,366	111,511	126,452
Net income available to common stockholders	$ 48,096	$ 33,593	$ 51,331	$ 26,346	$ 38,899	$ 26,691	$ 41,389	$ 4,532	$ 159,366	$ 111,511	$ 121,035
Net income per share	$ 0.94	$ 0.66	$ 1.01	$ 0.52	$ 0.76	$ 0.52	$ 0.81	$ 0.09	$ 3.12	$ 2.18	$ 2.38
Net income per share - assuming dilution	$ 0.94	$ 0.66	$ 1.00	$ 0.51	$ 0.75	$ 0.52	$ 0.80	$ 0.09	$ 3.11	$ 2.16	$ 2.17