Income Taxes (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Components of loss before income taxes                      
United States                 $ (88,112) $ (46,328) $ (23,522)
Foreign                 (1,670) (1,164) (1,316)
Net loss $ (24,360) $ (22,527) $ (24,258) $ (18,637) $ (15,305) $ (12,615) $ (10,539) $ (9,033) $ (89,782) $ (47,492) $ (24,838)
Reconciliation of the tax expense computed at the statutory federal rate and Company's tax expense                      
U.S. federal taxes at statutory rate                 34.00% 34.00% 34.00%
State taxes (net of federal benefit)                 0.80% 0.70% 0.90%
Non-deductible expenses                 0.80% 0.70% 0.40%
Foreign tax differential                 0.20% 0.80% 1.80%
Change in valuation allowance                 33.80% 33.20% 32.70%
Total                 0.00% 0.00% 0.00%
Deferred tax assets:                      
Net operating loss carryforwards 53,123       28,022       $ 53,123 $ 28,022  
Tax credits 13       13       13 13  
Accruals and other 7,612       1,914       7,612 1,914  
Gross deferred tax assets 60,748       29,949       60,748 29,949  
Valuation allowance (60,304)       (29,498)       (60,304) (29,498)  
Net deferred tax assets 444       451       444 451  
Deferred tax liabilities:                      
Property and equipment (444)       (451)       (444) (451)  
Total deferred tax liabilities $ (444)       $ (451)       $ (444) $ (451)