Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid In Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings
Balance at December 31, 2018 at Dec. 31, 2017	$ 237,473	$ 8	$ 519,435	$ 1,893	$ (283,863)
Beginning balance, Shares at Dec. 31, 2017		77,736,201
Issuance of common stock upon exercise of stock options	638		638
Issuance of common stock upon exercise of stock options, Shares		712,973
Issuance of common stock upon exercise of warrants, Shares		3,317
Release of restricted stock units		26,175
Stock-based compensation	4,924		4,924
Other comprehensive income (loss)	728			728
Cumulative effect of changes in accounting principlesrelated to revenue recognition	(25,310)				(25,310)
Net loss	(21,494)				(21,494)
Balance at March 31, 2019 at Mar. 31, 2018	196,959	$ 8	524,997	2,621	(330,667)
Beginning balance, Shares at Mar. 31, 2018		78,478,666
Balance at December 31, 2018 at Dec. 31, 2018	$ 135,311	$ 8	538,895	940	(404,532)
Beginning balance, Shares at Dec. 31, 2018	79,571,714	79,571,714
Issuance of common stock upon exercise of stock options	$ 251		251
Issuance of common stock upon exercise of stock options, Shares	254,481	254,481
Release of restricted stock units		25,850
Stock-based compensation	$ 3,703		3,703
Other comprehensive income (loss)	(449)			(449)
Net loss	(23,427)				(23,427)
Balance at March 31, 2019 at Mar. 31, 2019	$ 115,389	$ 8	$ 542,849	$ 491	$ (427,959)
Beginning balance, Shares at Mar. 31, 2019	79,852,045	79,852,045