Income Tax - Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets
Net operating losses	$ 3,912	$ 10,032	$ 9,666
Stock-based compensation	572	949	890
Intangible assets	2,190	3,748	3,752
Other	115	77	50
Total deferred tax assets	6,789	14,806	14,358
Valuation allowance	(462)	(14,497)	(14,358)
Deferred tax asset, net of valuation allowance	6,327	309	0
Deferred tax liability	(126)	(309)	0
Net deferred tax assets	$ 6,201	$ 0	$ 0