Quarterly Financial Summary (unaudited) (Details) - USD ($) $ / shares in Units, $ 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]
Revenue	$ 74,381	$ 67,888	$ 70,560	$ 73,441	$ 76,930	$ 72,992	$ 72,798	$ 74,967	$ 286,270	$ 297,687	$ 299,248
Income (loss) from operations before income taxes	9,310	(1,894)	6,813	2,435	12,419	7,658	8,709	6,655	16,664	35,441	35,044
Net income (loss)	$ 5,719	$ (1,638)	$ 4,921	$ 1,011	$ 9,093	$ 5,499	$ 6,458	$ 4,589	$ 10,013	$ 25,639	$ 21,121
Net income (loss) per common share:
Basic (in dollars per share)	$ 0.37	$ (0.10)	$ 0.30	$ 0.06	$ 0.55	$ 0.33	$ 0.39	$ 0.28	$ 0.62	$ 1.56	$ 1.30
Diluted (in dollars per share)	$ 0.37	$ (0.10)	$ 0.30	$ 0.06	$ 0.55	$ 0.33	$ 0.39	$ 0.28	$ 0.62	$ 1.54	$ 1.29