Accrued Expenses - (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Accrued Expenses
Payroll and related costs	$ 2,704	$ 2,498
Clinical and nonclinical trial expenses	2,838	3,577
Professional and consulting fees	476	840
Equipment purchase		368
Other	101	111
Total accrued expenses	6,119	$ 7,394
Salary continuation severance benefits	1,000
Long-term portion of other liabilities	$ 400