Quarterly Financial Data (Unaudited) - Quarterly Operating Results (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 Data [Abstract]
Revenue	$ 163,445	$ 146,815	$ 168,182	$ 147,953	$ 155,828	$ 154,246	$ 146,791	$ 141,425	$ 626,395	$ 598,290	$ 521,212
Gross profit	54,849	45,296	68,584	48,952	54,582	52,409	45,769	43,920	217,681	196,680
Operating income/(loss)	25,698	17,064	40,548	19,706	27,848	24,231	(763)	11,922	103,016	63,238	50,431
Net income	$ 17,346	$ 21,136	$ 29,100	$ 19,642	$ 33,391	$ 18,574	$ (3,367)	$ 6,391	$ 87,224	$ 54,989	$ 40,054
Net income per common share - basic (in dollars per share)	$ 0.20	$ 0.24	$ 0.34	$ 0.23	$ 0.40	$ 0.22	$ (0.04)	$ 0.08	$ 1.00	$ 0.66	$ 0.48
Net income (loss) per common share - diluted (in dollars per share)	$ 0.20	$ 0.24	$ 0.33	$ 0.22	$ 0.38	$ 0.22	$ (0.04)	$ 0.07	$ 0.98	$ 0.64	$ 0.47