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	Dec. 31, 2015	Dec. 31, 2014
Loss before income taxes
U.S. operations									$ (11,823)	$ (8,517)	$ (5,236)
Foreign operations									(8,740)
Net loss	$ (4,714)	$ (10,632)	$ (2,594)	$ (2,623)	$ (2,597)	$ (2,657)	$ (2,229)	$ (1,034)	$ (20,563)	$ (8,517)	$ (5,236)
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Federal statutory income tax rate									(34.00%)	(34.00%)	(34.00%)
State taxes, net of federal benefit									(3.80%)	(6.60%)	(6.60%)
Foreign rate differential									6.00%
Research and development tax credits									(1.50%)	(1.00%)	(1.60%)
Change in deferred tax asset valuation allowance									33.30%	41.60%	42.20%
Components of net deferred tax assets
Net operating loss carryforwards												$ 5,750	$ 5,606
Capitalized start-up costs												4,401
Research and development tax credit carryforwards												500	203
Capitalized research and development expenses												611	620
Intangible assets												1,650
Stock‑based compensation expenses												373	11
Other												1	4
Total deferred tax assets												13,286	6,444
Valuation allowance	(13,286)			(6,444)	(6,444)			(2,899)	$ (6,444)	$ (2,899)	$ (690)	(13,286)	(6,444)
Changes in valuation allowance for deferred tax assets
Valuation allowance at beginning of year				$ (6,444)				$ (2,899)	(6,444)	(2,899)	(690)
Increases recorded to income tax provision									(6,842)	(3,545)	(2,209)
Valuation allowance as of end of year	(13,286)				$ (6,444)				(13,286)	$ (6,444)	$ (2,899)
Unrecognized Tax Benefits
Increases related to prior year tax provisions									(2,624)
Increases related to current year tax provisions									(1,776)
Unrecognized Tax Benefits, Ending Balance	$ (4,400)								(4,400)
Unrecognized Tax Benefits that Would Impact Effective Tax Rate												0	$ 0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense									$ 0
Federal
Components of net deferred tax assets
Net operating loss carryforwards												13,917
Research and development tax credit carryforwards												500
State
Components of net deferred tax assets
Net operating loss carryforwards												13,917
Research and development tax credit carryforwards												$ 0