Quarterly Financial Information (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	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, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 222,116	$ 154,305	$ 111,312	$ 137,876	$ 146,183	$ 147,233	$ 144,275	$ 142,924	$ 136,327	$ 128,643	$ 124,626	$ 108,230	$ 625,609	$ 580,615	$ 497,826
Gross Profit	71,380	68,329	62,219	80,419	93,072	92,062	93,321	96,995	94,025	85,680	81,067	68,639
Operating income	27,740	31,899	31,850	34,313	34,253	26,007	41,282	54,131	41,530	39,238	38,315	33,896	125,802	155,673	152,979
Net income from continuing operations	$ 19,497	$ 24,682	$ 23,475	$ 24,723	$ 21,650	$ 20,509	$ 28,851	$ 25,710	$ 8,509	$ 29,242	$ 29,180	$ 26,208	$ 92,377	$ 96,720	$ 93,139
Basic (in dollars per share)	$ 0.64	$ 0.81	$ 0.77	$ 0.81	$ 0.71	$ 0.67	$ 0.95	$ 0.84	$ 0.27	$ 0.93	$ 0.93	$ 0.83	$ 3.03	$ 3.17	$ 2.97
Diluted (in dollars per share)	$ 0.64	$ 0.80	$ 0.76	$ 0.81	$ 0.71	$ 0.67	$ 0.94	$ 0.84	$ 0.27	$ 0.92	$ 0.92	$ 0.83	$ 3.02	$ 3.16	$ 2.95