Income Taxes - Net Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred tax liabilities:
Intangible assets	$ 1,764	$ 2,001	$ 2,247
Total deferred tax liabilities	1,764	2,001	2,247
Deferred tax assets:
Loss carryforwards	77,194	63,560	54,253
Capital loss carryforward	840	841	844
Property and equipment	1,096	1,135	1,149
License fees	8,351	7,055	5,393
Accrued expenses and other	886	602	412
Stock compensation	3,445	2,953	2,698
Total deferred tax assets before valuation allowance	91,812	76,146	64,749
Valuation allowance	(90,048)	(74,145)	(62,502)
Total deferred tax assets	1,764	2,001	2,247
Net deferred tax assets	$ 0	$ 0	$ 0