Income Taxes - Net Change in Total Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Balance at beginning of period	$ (58,542)	$ (45,011)	$ (34,357)
Tax valuation increase	(9,779)	(14,375)	(10,975)
Tax valuation decrease	269	844	321
Balance at end of period	$ (68,052)	$ (58,542)	$ (45,011)