Quarterly Financial Results (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, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 162,554	$ 157,678	$ 146,339	$ 145,562	$ 145,159	$ 144,684	$ 141,869	$ 133,815	$ 612,133	$ 565,527	$ 498,375
Total cost of revenues	99,647	96,704	91,155	93,217	89,392	89,235	89,515	86,071
Income from operations	15,414	15,665	11,739	12,436	15,613	15,808	13,381	10,530	55,254	55,332	35,944
Income before income taxes	11,604	8,529	9,693	10,503	13,739	13,903	11,527	8,772	40,329	47,941	32,372
Net income	$ 8,421	$ 6,177	$ 6,609	$ 8,974	$ 11,792	$ 9,779	$ 8,528	$ 7,026	$ 30,181	$ 37,125	$ 24,559
Earnings Per Share, Basic (in dollars per share)	$ 0.27	$ 0.19	$ 0.21	$ 0.28	$ 0.38	$ 0.31	$ 0.27	$ 0.22	$ 0.95	$ 1.18	$ 0.76
Earnings Per Share, Diluted (in dollars per share)	$ 0.26	$ 0.19	$ 0.20	$ 0.27	$ 0.36	$ 0.30	$ 0.27	$ 0.22	$ 0.93	$ 1.15	$ 0.73