Income Taxes - Deferred taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current, Assets
Accrued Expenses	$ 2,950	$ 2,995
Other		45
Subtotal	2,950	3,040
Valuation allowance	(2,918)	(3,040)
Total current deferred taxes	32
Net current deferred taxes
Current, Liabilities
Other	(32)
Net current deferred taxes	(32)
Long Term, Assets
Net operating loss carryforwards	31,971	13,063
Capital loss carryforward	77	113
Research & development credit	23,391	13,733
State research and development credit	1,994
Capitalized research and development	34,472	11,797
Amortization	2,746	1,423
Stock options and warrants	9,370	6,264
Subtotal	104,021	46,393
Valuation allowance	(102,547)	(46,376)
Total long-term deferred taxes	1,474	17
Long Term, Liabilities
Fixed assets	(1,474)	(17)
Subtotal	(1,474)	(17)
Total long-term deferred taxes	$ (1,474)	$ (17)