Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jan. 01, 2016	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Income tax provision	$ 655	$ 606	$ 640
Statutory federal rate	34.00%	34.00%	34.00%
Valuation allowance	$ 115,689	$ 84,167	$ 64,449		$ 47,858
Full valuation allowance against tax benefits	124,872	$ 95,397
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	176,500
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	250,200
Federal | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research and development tax credit carryforwards	$ 800
Adjustments for New Accounting Principle, Early Adoption
Operating Loss Carryforwards [Line Items]
Full valuation allowance against tax benefits				$ 18,000