Stockholders' Equity - Warrants to Purchase Common Stock (Details) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017
Class of Warrant or Right [Line Items]
Number of common stock that can be purchased (shares)		37,840
Exercise price of warrants (in usd per share)		$ 76.11
Warrants From July 2012 Public Offering [Member]
Class of Warrant or Right [Line Items]
Number of common stock that can be purchased (shares)	1,901,918
Exercise price of warrants (in usd per share)	$ 20.00
Term of common stock warrant exercisable	5 years