Stock Option Plans and Stock-Based Compensation - Schedule of Stock-Based Compensation Expense Related to Founder's Shares (Details) - Restricted Common Stock (Founders Shares) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 9	$ 1,551	$ 1,281
Research and Development Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 9	1,547	227
General and Administrative Expense
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense		$ 4	$ 1,054