Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Increase (decrease) in valuation allowance	$ (28,500)	$ 5,800
Increase in domestic valuation allowance	5,914	$ 10,162
Impact of federal rate change on valuation allowance	34,400
Impact of federal rate change	34,500
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	237,900
Domestic Tax Authority | Research and development
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	1,400
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 300