Public Offering (Details) - USD ($) $ / shares in Units, $ in Millions				12 Months Ended
	Jun. 14, 2017	May 15, 2017	May 09, 2017	Dec. 31, 2017
Common stock
Class of Stock [Line Items]
Issuance of common stock and warrants (shares)				3,085,000
Shares to the public
Class of Stock [Line Items]
Sale of stock (shares)		2,750,000
Underwriters
Class of Stock [Line Items]
Sale of stock (shares)	335,484
Underwriters | Common stock
Class of Stock [Line Items]
Issuance of common stock and warrants (shares)			412,500
Public offering
Class of Stock [Line Items]
Public offering price (dollars per share)			$ 28.85
Underwriting discounts and commissions (dollars per share)			$ 1.73
Gross proceeds from sale of common stock	$ 89.0
Underwriting discounts, commissions and other costs	5.8
Net proceeds	$ 83.2