Income Taxes, Valuation Allowance, Operating Loss Carryforwards and Tax Credit Carry-forwards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Abstract]
Net change in valuation allowance	$ 2,271
Income Taxes [Abstract]
Net operating loss carryforwards	25,000	$ 17,000	$ 28,000
Federal [Member]
Income Taxes [Abstract]
Net operating loss carryforwards	$ 112,709
Operating loss carryforwards, expiration dates	Dec. 31, 2027
Federal [Member] | Research and Development [Member]
Tax credit carryforwards [Abstract]
Tax credit carryforwards	$ 1,635
Federal tax credit carryforward, expiration dates	Dec. 31, 2031
State [Member]
Income Taxes [Abstract]
Net operating loss carryforwards	$ 107,948
Operating loss carryforwards, expiration dates	Dec. 31, 2028