Convertible Note Payable - Additional Information (Details) - USD ($)		12 Months Ended
	Jan. 29, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Oct. 31, 2012
Debt Instrument [Line Items]
Number of shares resulting from conversion of note payable	1,356,738
Conversion price per share (dollars per share)	$ 4.00
Loss from valuation of convertible note payable		$ 0	$ (1,811,000)	$ (12,118,000)
Convertible Debt | GSK
Debt Instrument [Line Items]
Notes payable					$ 5,400,000