Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - 9 months ended Sep. 30, 2018 - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]
Beginning Balance at Dec. 31, 2017	$ 109,842	$ 54	$ 755,526	$ 343	$ (646,081)
Beginning Balance, shares at Dec. 31, 2017		53,960,832
Stock-based compensation	7,480	$ 0	7,480	0	0
Exercise of stock options, value	3,113	$ 1	3,112	0	0
Exercise of stock options, shares		415,263
Issuance of common stock under Employee Stock Purchase Plan, value	536	$ 0	536	0	0
Issuance of common stock under Employee Stock Purchase Plan, shares		75,992
Vesting of restricted stock units, net of taxes withheld, value	(866)	$ 0	(866)	0	0
Vesting of restricted stock units, net of taxes withheld, shares		189,433
Issuance of warrants	182	$ 0	182	0	0
Other comprehensive income	104	0	0	104	0
Adoption of ASC 606 | ASC 606 [Member]	11,499	0	0	0	11,499
Net loss	(79,821)	0	0	0	(79,821)
Ending Balance at Sep. 30, 2018	$ 52,069	$ 55	$ 765,970	$ 447	$ (714,403)
Ending Balance, shares at Sep. 30, 2018		54,641,520