Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 72,095	$ 75,526	$ 72,822	$ 64,856	$ 57,661	$ 56,440	$ 50,080	$ 47,774	$ 285,299	$ 211,955	$ 166,806
Gross profit	51,138	52,923	53,701	48,599	42,192	42,766	38,957	36,451
(Loss) from operations	1,918	10,110	11,024	2,238	861	9,136	2,322	2,183	25,290	14,502	(17,064)
Net loss	$ (10,345)	$ 4,347	$ (5,310)	$ (9,538)	$ (8,520)	$ (4,090)	$ (20,110)	$ (12,386)	$ (20,846)	$ (45,106)	$ (81,374)
Basic	$ (0.29)	$ 0.12	$ (0.15)	$ (0.30)	$ (0.37)	$ (0.18)	$ (0.87)	$ (0.53)	$ (0.61)	$ (1.94)	$ (3.51)
Diluted	$ (0.29)	$ 0.12	$ (0.15)	$ (0.30)	$ (0.37)	$ (0.18)	$ (0.87)	$ (0.53)	$ (0.61)	$ (1.94)	$ (3.51)