Shareholders’ Equity (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended				3 Months Ended	9 Months Ended	12 Months Ended
	Aug. 31, 2018	Apr. 30, 2018	Mar. 31, 2018	Aug. 31, 2017	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017	May 31, 2018	Oct. 31, 2017
Common Stock [Member]
Class of Stock [Line Items]
Authorized number of shares for issuance in offering program									2,000,000
Issuance of common stock						100,000
Payments of sales commissions						$ 0.1
Proceeds from issuance of stock						$ 2.8
Remaining number of shares for issuance in offering program					1,000,000	1,000,000
Series A Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred shares issued		170,900	1,600,000		2,199,610	2,199,610	0
Preferred shares dividend rate			8.50%			8.50%	8.50%
Preferred shares, par value			$ 0.0001
Preferred shares, liquidation preference			25.00
Preferred shares, redemption price			$ 25.00
Net proceeds from issuance of preferred shares		$ 4.1	$ 38.3		$ 10.5
Payments of underwriting discount		$ 0.1
Authorized number of shares for issuance in offering program								2,200,000
Issuance of common stock					428,710
Payments of sales commissions					$ 0.2
Remaining number of shares for issuance in offering program					1,800,000	1,800,000
Series B Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred shares issued	1,700,000				1,955,000	1,955,000	0
Preferred shares dividend rate	8.50%					8.50%	8.50%
Preferred shares, par value	$ 0.0001
Preferred shares, liquidation preference	$ 25.00
Preferred shares, redemption price				$ 25.00
Net proceeds from issuance of preferred shares	$ 41.2
Preferred shares issued, additional offering	255,000
Net proceeds from issuance of preferred shares, additional offering	$ 6.2
Payments of underwriting discount	$ 0.2
LIBOR [Member] | Series A Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred shares, variable dividend rate			5.82%
LIBOR [Member] | Series B Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Stock [Member]
Class of Stock [Line Items]
Preferred shares, variable dividend rate						5.69%