Condensed Consolidated Statement of Stockholders' Equity (Unaudited) - 3 months ended Mar. 31, 2018 - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Deficit
Balance at Dec. 31, 2017	$ 152,279	$ 10	$ 436,278	$ (671)	$ (283,338)
Balance, Shares at Dec. 31, 2017		99,157
Vesting of early exercised stock options	106		106
Issuance of common stock upon exercise of stock options, net	$ 4,997		5,049	(52)
Issuance of common stock upon exercise of stock options, net, Shares	1,670	1,670
Issuance of common stock pursuant to exercise of common warrants, net, Shares		141
Stock-based compensation expense	$ 4,429		4,429
Cumulative effect change in accounting principle | Accounting Standards Update 2016-16	(40)				(40)
Cumulative effect change in accounting principle | Accounting Standards Update 2014-09	38,339				38,339
Net loss	(6,634)				(6,634)
Balance at Mar. 31, 2018	$ 193,476	$ 10	$ 445,862	$ (723)	$ (251,673)
Balance, Shares at Mar. 31, 2018		100,968