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Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Taxes [Abstract]
Income tax expense	$ 5	$ 5
Net change in valuation allowance	4,796	$ 1,786
Valuation allowance carried against net deferred tax assets	39,000		$ 34,000
ASU 2014-09 [Member]
Operating Loss Carryforwards [Line Items]
Deferred revenue recognized			$ 2,500
Federal [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 94,000
Federal [Member] \| Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, expiration dates	Dec. 31, 2027
State [Member]
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 108,000
State [Member] \| Earliest Tax Year [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, expiration dates	Dec. 31, 2028