Selected Quarterly Financial Data (unaudited) - Schedule of Selected Quarterly Statements of Income Data (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 193,409	$ 175,006	$ 169,313	$ 199,943	$ 150,332	$ 133,288	$ 128,800	$ 153,916	$ 737,671	$ 566,336	$ 433,047
Operating income	60,294	50,556	52,886	62,488	43,413	36,245	43,037	51,020	226,224	173,715	129,710
Net income	$ 45,380	$ 39,152	$ 48,762	$ 47,282	$ 31,414	$ 28,769	$ 35,722	$ 41,160	$ 180,576	$ 137,065	$ 123,486
Earnings per share, basic	$ 0.79	$ 0.68	$ 0.85	$ 0.82	$ 0.55	$ 0.50	$ 0.62	$ 0.71	$ 3.14	$ 2.37	$ 2.13
Earnings per share, diluted	$ 0.78	$ 0.67	$ 0.83	$ 0.81	$ 0.54	$ 0.49	$ 0.61	$ 0.70	$ 3.09	$ 2.34	$ 2.10
Weighted average shares outstanding:
Basic	57,659	57,654	57,569	57,357	57,491	57,727	57,837	57,793	57,561	57,711	57,839
Diluted	58,378	58,383	58,410	58,316	58,238	58,545	58,721	58,739	58,395	58,582	58,790