Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Loss Carryforwards [Line Items]
Income tax (benefit) provision	$ (2,164)	$ 655	$ 606
Impact from the change in tax law	2,632	0	0
Remeasurement of our U.S. federal deferred tax assets and liabilities	1,200
Release of valuation allowance due to the Tax Act	$ 1,398	$ 0	$ 0
Statutory federal rate	34.00%	34.00%	34.00%
Valuation allowance	$ 107,046	$ 115,689	$ 84,167	$ 64,449
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	247,500
State and Local Jurisdiction | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credit carryforwards	400
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	393,600
Federal | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credit carryforwards	$ 800