CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN STOCKHOLDERS' EQUITY - 6 months ended Jun. 30, 2018 - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Convertible Note 2023	Convertible Note 2023 Additional Paid-in Capital
Balance (in shares) at Dec. 31, 2017		53,400,281
Balance at Dec. 31, 2017	$ 44,753	$ 554	$ 106,312	$ (2,019)	$ (60,094)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation expense	1,165		1,165
Stock options exercised (in shares)		11,000
Stock options exercised	12		12
Issuance of stock for vested restricted stock units (in shares)		101,607
Fair value of conversion feature on Convertible 4.75% Senior Notes						$ 18,637	$ 18,637
Partial extinguishment of equity component of Convertible 3.75% Senior Notes	7,600					$ (7,602)	$ (7,602)
Cumulative translation adjustment	(332)			(332)
Net loss	(17,921)
Balance (in shares) at Jun. 30, 2018		53,512,888
Balance at Jun. 30, 2018	$ 38,712	$ 554	$ 118,524	$ (2,351)	$ (78,015)