Warrants - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant exercise price (in dollars per share)		$ 4.85		$ 4.85		$ 5.98
Warrant | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-cash income (expense)		$ 5.0	$ 3.0	$ (4.7)	$ 10.5
Issued in 2017 Series A Preferred Stock Offering
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants issued to purchase common stock (in shares)	3,437,334
Warrant exercise price (in dollars per share)	$ 2.54
Period after date of issuance to be exercised	6 months
Exercise period	5 years