Public Offerings (Details) - USD ($) $ / shares in Units, $ in Thousands						12 Months Ended
	Jun. 14, 2017	May 15, 2017	May 09, 2017	Dec. 15, 2015	Dec. 09, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Public offering price (dollars per share)					$ 17	$ 26.20
Underwriting discount and commission fees (dollars per share)					$ 1.19
Gross proceeds from sale of common stock				$ 109,300
Stock issuance costs				5,900		$ 0	$ 814	$ 0
Proceeds from common stock issuance				$ 103,400
Common stock
Class of Stock [Line Items]
Issuance of common stock and warrants (shares)				6,400,000		3,085,000		6,426,000
Common stock | Affiliated entity
Class of Stock [Line Items]
Issuance of common stock and warrants (shares)					2,900,000
Public offering | Common stock
Class of Stock [Line Items]
Issuance of common stock and warrants (shares)					5,600,000
Underwriters
Class of Stock [Line Items]
Sale of stock (shares)	335,000
Underwriters | Common stock
Class of Stock [Line Items]
Issuance of common stock and warrants (shares)			413,000		838,000
Offering exempt from underwriter commission | Common stock | Affiliated entity
Class of Stock [Line Items]
Issuance of common stock and warrants (shares)					2,400,000
Shares to the public | Pro-forma
Class of Stock [Line Items]
Sale of stock (shares)		2,800,000
Public offering
Class of Stock [Line Items]
Gross proceeds from sale of common stock	$ 89,000
Public offering price (dollars per share)			$ 28.85
Underwriting discounts and commissions (dollars per share)			$ 1.731
underwriting discounts, commissions and other costs	5,800
Net proceeds	$ 83,200
Public offering | Pro-forma
Class of Stock [Line Items]
Sale of stock (shares)			3,200,000