Condensed Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Cumulative Distributions in Excess of Earnings
Beginning balance at Dec. 31, 2016	$ 452,430	$ 648	$ 611,475	$ (159,693)
Beginning balance (in shares) at Dec. 31, 2016		64,816,350
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net	170,319	$ 106	170,213
Issuance of common stock, net, (in shares)		10,573,089
Vesting of restricted common stock, net of shares withheld for employee taxes	(866)	$ 1	(867)
Vesting of restricted common stock, net of shares withheld for employee taxes (in shares)		88,763
Amortization of stock-based compensation	2,416		2,416
Common dividends ($0.615 and $0.74 per share for the nine months ended 9/30/2018 and year ended 12/31/2017, respectively) (in usd per share)	(55,556)			(55,556)
Net income	25,874			25,874
Ending balance at Dec. 31, 2017	594,617	$ 755	783,237	(189,375)
Ending balance (in shares) at Dec. 31, 2017		75,478,202
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net	130,550	$ 78	130,472
Issuance of common stock, net, (in shares)		7,760,723
Vesting of restricted common stock, net of shares withheld for employee taxes	(1,289)	$ 1	(1,290)
Vesting of restricted common stock, net of shares withheld for employee taxes (in shares)		114,301
Amortization of stock-based compensation	2,816		2,816
Common dividends ($0.615 and $0.74 per share for the nine months ended 9/30/2018 and year ended 12/31/2017, respectively) (in usd per share)	(49,028)			(49,028)
Net income	42,384			42,384
Ending balance at Sep. 30, 2018	$ 720,050	$ 834	$ 915,235	$ (196,019)
Ending balance (in shares) at Sep. 30, 2018		83,353,226