Quarterly Financial Information (Unaudited) - Summary of Selected Unaudited Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 52,367	$ 46,996	$ 45,225	$ 43,931	$ 44,320	$ 40,627	$ 38,779	$ 36,843	$ 188,519	$ 160,569	$ 129,251
Gross profit	37,682	33,066	30,706	28,512	29,900	26,638	25,624	24,247	129,966	106,409	80,074
Net loss	$ (6,890)	$ (5,171)	$ (7,013)	$ (6,547)	$ (7,917)	$ (8,755)	$ (8,985)	$ (5,896)	$ (25,621)	$ (31,553)	$ (41,007)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.17)	$ (0.13)	$ (0.18)	$ (0.17)	$ (0.21)	$ (0.63)	$ (0.69)	$ (0.45)	$ (0.64)	$ (1.61)	$ (3.24)