Selected Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Selected Quarterly Financial Information [Abstract]
Revenue	$ 91,104	$ 81,748	$ 81,102	$ 68,586	$ 76,871	$ 71,121	$ 73,214	$ 71,688	$ 322,540	$ 292,894	$ 411,423
Gross profit	22,586	18,933	15,472	9,182	15,686	10,513	16,777	18,503	66,173	61,479	117,133
Net loss	$ (6,729)	$ (8,125)	$ (10,537)	$ (18,246)	$ (14,283)	$ (18,187)	$ (9,341)	$ (11,522)	$ (43,637)	$ (53,333)	$ (205)
Basic net loss per share (USD per share)	$ (0.15)	$ (0.18)	$ (0.24)	$ (0.41)	$ (0.32)	$ (0.42)	$ (0.22)	$ (0.27)	$ (0.97)	$ (1.23)	$ 0.00
Diluted net loss per share (USD per share)	$ (0.15)	$ (0.18)	$ (0.24)	$ (0.41)	$ (0.32)	$ (0.42)	$ (0.22)	$ (0.27)	$ (0.97)	$ (1.23)	$ 0.00
Weighted average shares used to compute basic net loss per share (in shares)	46,150	45,476	44,665	44,259	44,079	43,790	43,219	42,615	45,144	43,431	41,798
Weighted average shares used to compute diluted net loss per share (in shares)	46,150	45,476	44,665	44,259	44,079	43,790	43,219	42,615	45,144	43,431	41,798