Preferred Stock - Narrative (Details) - USD ($)			3 Months Ended	6 Months Ended		12 Months Ended
	Jan. 23, 2018	Mar. 15, 2017	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Jul. 21, 2017
Class of Stock [Line Items]
Preferred stock shares issued (in shares)			3,707,256	3,707,256		1,704,339
Preferred stock par value per share (in dollars per share)			$ 0.01	$ 0.01		$ 0.01
Proceeds from issuance of Series A Preferred Stock, net of issuance costs paid	$ 48,900,000	$ 39,000,000		$ 48,490,000	$ 37,937,000
Preferred offering expenses (less than)	$ 500,000	$ 1,000,000
Aggregate offering price							$ 50,000,000.0
Preferred stock shares outstanding (in shares)			3,707,256	3,707,256		1,704,339
Dividends paid				$ 4,055,000
LIBOR
Class of Stock [Line Items]
Preferred stock dividend accrual rate		8.75%
Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock shares issued (in shares)	2,000,000	1,610,000
Preferred stock stated rate (percent)		8.75%
Preferred stock par value per share (in dollars per share)		$ 0.01
Preferred stock liquidation preference (in dollars per share)		25.00
Preferred stock price to the public (in dollars per share)	$ 25.25	25.00
Preferred stock price, net of underwriting discounts and commissions (in dollars per share)	$ 24.45	$ 24.21
Dividends paid			$ 2,000,000	2,900,000
Dividend accrual			$ 2,000,000	$ 2,000,000
Series A Preferred Stock | ATM Agreement
Class of Stock [Line Items]
Preferred stock shares issued (in shares)			2,917	2,917		94,339
Proceeds from issuance of Series A Preferred Stock, net of issuance costs paid				$ 100,000		$ 2,400,000
Preferred offering expenses (less than)				$ 100,000		$ 100,000