Accrued Expenses - Components of Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Payables And Accruals [Abstract]
Accrued clinical	$ 4,536	$ 2,132
Accrued bonus	2,178	1,286
Professional fees	647	328
Accrued payroll	518	213
Accrued vacation	310	177
Accrued severance		179
Other	1,366	549
Total accrued expenses	$ 9,555	$ 4,864