Summarized Condensed Consolidating Information - Condensed Consolidating Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Assets:
Real estate investments, net	$ 1,177,140	$ 1,152,261
Other real estate investments, net	18,031	17,949
Cash and cash equivalents	14,195	6,909	$ 1,283	$ 7,500
Accounts and other receivables, net	5,999	5,254
Prepaid expenses and other assets	1,919	895
Deferred financing costs, net	1,447	1,718
Investment in subsidiaries	0	0
Intercompany	0	0
Total assets	1,218,731	1,184,986
Liabilities and Equity:
Senior unsecured notes payable, net	294,584	294,395
Senior unsecured term loan, net	99,540	99,517
Unsecured revolving credit facility	200,000	165,000
Accounts payable and accrued liabilities	15,111	17,413
Dividends payable	15,608	14,044
Intercompany	0	0
Total liabilities	624,843	590,369
Equity:
Common stock, $0.01 par value; 500,000,000 shares authorized, 75,522,046 and 75,478,202 shares issued and outstanding as of March 31, 2018 and December 31, 2017, respectively	755	755
Additional paid-in capital	783,509	783,237
Cumulative distributions in excess of earnings	(190,376)	(189,375)
Total equity	593,888	594,617		452,430
Total liabilities and equity	1,218,731	1,184,986
Reportable Legal Entities | Parent Guarantor
Assets:
Real estate investments, net	0	0
Other real estate investments, net	0	0
Cash and cash equivalents	0	0	0	0
Accounts and other receivables, net	0	0
Prepaid expenses and other assets	0	0
Deferred financing costs, net	0	0
Investment in subsidiaries	609,496	619,075
Intercompany	0	0
Total assets	609,496	619,075
Liabilities and Equity:
Senior unsecured notes payable, net	0	0
Senior unsecured term loan, net	0	0
Unsecured revolving credit facility	0	0
Accounts payable and accrued liabilities	0	0
Dividends payable	15,608	14,044
Intercompany	0	0
Total liabilities	15,608	14,044
Equity:
Common stock, $0.01 par value; 500,000,000 shares authorized, 75,522,046 and 75,478,202 shares issued and outstanding as of March 31, 2018 and December 31, 2017, respectively	755	755
Additional paid-in capital	783,509	783,237
Cumulative distributions in excess of earnings	(190,376)	(178,961)
Total equity	593,888	605,031
Total liabilities and equity	609,496	619,075
Reportable Legal Entities | Issuers
Assets:
Real estate investments, net	835,324	805,826
Other real estate investments, net	12,387	12,399
Cash and cash equivalents	14,195	6,909	1,283	7,500
Accounts and other receivables, net	3,875	2,945
Prepaid expenses and other assets	1,916	893
Deferred financing costs, net	1,447	1,718
Investment in subsidiaries	454,075	444,120
Intercompany	0	0
Total assets	1,323,219	1,274,810
Liabilities and Equity:
Senior unsecured notes payable, net	294,584	294,395
Senior unsecured term loan, net	99,540	99,517
Unsecured revolving credit facility	200,000	165,000
Accounts payable and accrued liabilities	12,789	15,176
Dividends payable	0	0
Intercompany	106,810	92,061
Total liabilities	713,723	666,149
Equity:
Common stock, $0.01 par value; 500,000,000 shares authorized, 75,522,046 and 75,478,202 shares issued and outstanding as of March 31, 2018 and December 31, 2017, respectively	0	0
Additional paid-in capital	531,420	546,097
Cumulative distributions in excess of earnings	78,076	62,564
Total equity	609,496	608,661
Total liabilities and equity	1,323,219	1,274,810
Reportable Legal Entities | Combined Subsidiary Guarantors
Assets:
Real estate investments, net	341,816	346,435
Other real estate investments, net	5,644	5,550
Cash and cash equivalents	0	0	0	0
Accounts and other receivables, net	2,124	2,309
Prepaid expenses and other assets	3	2
Deferred financing costs, net	0	0
Investment in subsidiaries	0	0
Intercompany	106,810	92,061
Total assets	456,397	446,357
Liabilities and Equity:
Senior unsecured notes payable, net	0	0
Senior unsecured term loan, net	0	0
Unsecured revolving credit facility	0	0
Accounts payable and accrued liabilities	2,322	2,237
Dividends payable	0	0
Intercompany	0	0
Total liabilities	2,322	2,237
Equity:
Common stock, $0.01 par value; 500,000,000 shares authorized, 75,522,046 and 75,478,202 shares issued and outstanding as of March 31, 2018 and December 31, 2017, respectively	0	0
Additional paid-in capital	321,761	321,761
Cumulative distributions in excess of earnings	132,314	122,359
Total equity	454,075	444,120
Total liabilities and equity	456,397	446,357
Elimination
Assets:
Real estate investments, net	0	0
Other real estate investments, net	0	0
Cash and cash equivalents	0	0	$ 0	$ 0
Accounts and other receivables, net	0	0
Prepaid expenses and other assets	0	0
Deferred financing costs, net	0	0
Investment in subsidiaries	(1,063,571)	(1,063,195)
Intercompany	(106,810)	(92,061)
Total assets	(1,170,381)	(1,155,256)
Liabilities and Equity:
Senior unsecured notes payable, net	0	0
Senior unsecured term loan, net	0	0
Unsecured revolving credit facility	0	0
Accounts payable and accrued liabilities	0	0
Dividends payable	0	0
Intercompany	(106,810)	(92,061)
Total liabilities	(106,810)	(92,061)
Equity:
Common stock, $0.01 par value; 500,000,000 shares authorized, 75,522,046 and 75,478,202 shares issued and outstanding as of March 31, 2018 and December 31, 2017, respectively	0	0
Additional paid-in capital	(853,181)	(867,858)
Cumulative distributions in excess of earnings	(210,390)	(195,337)
Total equity	(1,063,571)	(1,063,195)
Total liabilities and equity	$ (1,170,381)	$ (1,155,256)