Income Taxes - Tax Effects of Temporary Differences (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Accrued liabilities not currently deductible	$ 1,542	$ 2,479
Intangible assets-excess of tax basis over financial statement basis	21,327	37,693
Federal impact of deferred state taxes	(2,011)	(3,242)
Net operating losses	45,268	52,367
Stock-based compensation	2,152	3,640
Other	399	408
Gross deferred tax assets	68,677	93,345
Deferred tax liabilities:
Intangible assets-excess of financial statement basis over tax basis	(332)	(677)
Property and equipment	(755)	(1,169)
Deferred gain on sale		(1,555)
Gross deferred tax liabilities	(1,087)	(3,401)
Valuation allowance	(67,630)	(90,052)
Net deferred tax liabilities	(40)	(108)
Non-current	$ (40)	$ (108)