Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Increase (decrease) in valuation allowance	$ 4,800	$ (28,500)
Increase in domestic valuation allowance	4,815	5,914
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	251,000
Net operating loss carryforwards, subject to expiration	237,500
Net operating loss carryforwards, not subject to expiration	13,500
Domestic Tax Authority | Research and development
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	1,900
Foreign Tax Authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	$ 300