Summary of Significant Accounting Policies - Loss Per Share of Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Basic and diluted net loss per share of common stock:
Net loss									$ (28,643)	$ (24,850)	$ (10,833)
Dividends on Series B and C Preferred Stock											(2,545)
Net loss applicable to common stockholders	$ (6,014)	$ (6,464)	$ (8,949)	$ (7,216)	$ (7,607)	$ (4,963)	$ (5,273)	$ (7,007)	$ (28,643)	$ (24,850)	$ (13,378)
Weighted average shares of common stock outstanding (in shares)									19,498,143	14,919,783	6,152,669
Net loss per share of common stock-basic and diluted (in dollars per share)	$ (0.31)	$ (0.33)	$ (0.46)	$ (0.37)	$ (0.45)	$ (0.35)	$ (0.37)	$ (0.50)	$ (1.47)	$ (1.67)	$ (2.17)
Antidilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)									2,434,944	1,799,226	1,670,574
Restricted stock
Basic and diluted net loss per share of common stock:
Antidilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)									195,900
Stock options
Basic and diluted net loss per share of common stock:
Antidilutive securities excluded from the computation of diluted weighted average shares outstanding (in shares)									2,239,044	1,799,226	1,670,574