Quarterly Consolidated Financial Data (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]
Revenues	$ 89,346	$ 85,776	$ 85,705	$ 86,510	$ 86,271	$ 88,900	$ 85,573	$ 82,630	$ 347,337	$ 343,374	$ 331,378
Gross profit	44,565	41,589	44,573	44,084	43,845	44,885	43,846	42,309	174,811	174,885	162,135
Net income	$ 10,450	$ 4,856	$ 6,412	$ 9,949	$ 13,293	$ 9,269	$ 9,745	$ 8,211	$ 31,667	$ 40,518	$ 123,385
Basic income per weighted-average share (in dollars per share)	$ 0.27	$ 0.12	$ 0.16	$ 0.26	$ 0.35	$ 0.24	$ 0.25	$ 0.22	$ 0.81	$ 1.06	$ 3.31
Diluted income per weighted-average share (in dollars per share)	$ 0.26	$ 0.12	$ 0.16	$ 0.25	$ 0.34	$ 0.24	$ 0.25	$ 0.21	$ 0.79	$ 1.03	$ 3.17