Income Taxes (Deferred Tax Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes
Valuation allowance increase	$ 24,500	$ 900	$ 10,800
Deferred tax assets
Net operating loss carryforwards	41,451	21,587
Research and development tax credit carryforwards	4,794	2,696
Reserves and accruals	3,108	1,717
Stock based compensation	2,206	1,505
Total deferred tax assets before valuation allowance	51,559	27,505
Less: valuation allowance	(51,153)	(26,627)
Deferred tax assets, net	406	878
Deferred tax liabilities
Property and equipment	$ (406)	$ (878)