Quarterly Results of Operations (unaudited) - 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 Results of Operations (unaudited)
Revenue	$ 107,723	$ 69,453	$ 74,305	$ 91,477	$ 105,683	$ 95,374	$ 119,333	$ 122,185	$ 342,958	$ 442,575	$ 410,561
Gross profit	44,316	30,581	31,749	37,506	43,567	39,913	49,000	47,156	144,152	179,636	150,247
Net income	$ 9,712	$ 704	$ 556	$ 6,062	$ 8,463	$ 8,838	$ 14,669	$ 13,915	$ 17,034	$ 45,885	$ 126,959
Net income per basic share (in dollars per share)	$ 0.30	$ 0.02	$ 0.02	$ 0.19	$ 0.26	$ 0.27	$ 0.46	$ 0.43	$ 0.52	$ 1.42	$ 4.11
Net income per diluted share (in dollars per share)	$ 0.29	$ 0.02	$ 0.02	$ 0.18	$ 0.25	$ 0.26	$ 0.43	$ 0.41	$ 0.50	$ 1.35	$ 3.80