Income Taxes - Deferred Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2014
Deferred tax assets:
Net operating loss carryforwards	$ 19,510	$ 9,831
Amortization	20,642	7,563
Stock based compensation	4,587	4,375
Fair value royalty agreements	0	635
Fair value contingent consideration	384	870
Other	479	406
Gross deferred tax assets	45,602	23,680
Deferred tax liabilities:
Amortization	(308)	(2,419)
Accounts receivable	(661)	(936)
Prepaid expenses	(405)	(1,094)
Gross deferred tax liabilities	(1,374)	(4,449)
Less: valuation allowances	(21,199)	(15,354)
Net deferred tax assets	$ 23,029	$ 3,877	$ 10,342	$ 13,102