Stockholders' Equity - Series A Preferred Stock (Details) - Series A Preferred Stock - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
	May 20, 2016	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Value of shares redeemed		$ 13.8	$ 2.8
Number of shares redeemed (in shares)		83,502	18,498
Reduction in the original recorded value of preferred stock		$ 8.4	$ 1.8
Reduction in the accretive value of the preferred stock		$ 5.4	$ 1.0
Private Placement
Class of Stock [Line Items]
Shares issued (in shares)	102,000
Price per share (in dollars per share)	$ 100.00
Aggregate proceeds from private placement	$ 10.2
Issuance costs	$ 0.7