Summarized Condensed Consolidating Information - Condensed Consolidating Statements of Cash Flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net cash (used in) provided by operating activities	$ 72,390	$ 66,933
Cash flows from investing activities:
Acquisitions of real estate	(75,621)	(222,463)
Improvements to real estate	(5,401)	(621)
Purchases of equipment, furniture and fixtures	(1,262)	(359)
Investment in real estate mortgage and other loans receivable	(2,598)	0
Principal payments received on real estate mortgage and other loans receivable	893	0
Escrow deposits for acquisitions of real estate	(1,000)	(1,000)
Net proceeds from the sale of real estate	13,004	0
Sale of other real estate investment	0	7,500
Distribution from subsidiary	0	0
Intercompany financing	0	0
Net cash used in investing activities	(71,985)	(216,943)
Cash flows from financing activities:
Proceeds from the issuance of common stock, net	130,546	170,414
Proceeds from the issuance of senior unsecured notes payable	0	300,000
Borrowings under unsecured revolving credit facility	60,000	158,000
Payments on senior unsecured notes payable	0	(267,639)
Payments on unsecured revolving credit facility	(135,000)	(158,000)
Payments of deferred financing costs	0	(6,047)
Net-settle adjustment on restricted stock	(1,288)	(866)
Dividends paid on common stock	(45,827)	(38,544)
Distribution to Parent	0	0
Intercompany financing	0	0
Net cash provided by financing activities	8,431	157,318
Net increase in cash and cash equivalents	8,836	7,308
Cash and cash equivalents, beginning of period	6,909	7,500
Cash and cash equivalents, end of period	15,745	14,808
Reportable Legal Entities | Parent Guarantor
Cash flows from operating activities:
Net cash (used in) provided by operating activities	(7)	(157)
Cash flows from investing activities:
Acquisitions of real estate	0	0
Improvements to real estate	0	0
Purchases of equipment, furniture and fixtures	0	0
Investment in real estate mortgage and other loans receivable	0
Principal payments received on real estate mortgage and other loans receivable	0
Escrow deposits for acquisitions of real estate	0	0
Net proceeds from the sale of real estate	0
Sale of other real estate investment		0
Distribution from subsidiary	45,827	38,544
Intercompany financing	(129,251)	(169,391)
Net cash used in investing activities	(83,424)	(130,847)
Cash flows from financing activities:
Proceeds from the issuance of common stock, net	130,546	170,414
Proceeds from the issuance of senior unsecured notes payable		0
Borrowings under unsecured revolving credit facility	0	0
Payments on senior unsecured notes payable		0
Payments on unsecured revolving credit facility	0	0
Payments of deferred financing costs		0
Net-settle adjustment on restricted stock	(1,288)	(866)
Dividends paid on common stock	(45,827)	(38,544)
Distribution to Parent	0	0
Intercompany financing	0	0
Net cash provided by financing activities	83,431	131,004
Net increase in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Reportable Legal Entities | Issuers
Cash flows from operating activities:
Net cash (used in) provided by operating activities	28,087	17,946
Cash flows from investing activities:
Acquisitions of real estate	(75,621)	(222,463)
Improvements to real estate	(5,376)	(571)
Purchases of equipment, furniture and fixtures	(1,193)	(292)
Investment in real estate mortgage and other loans receivable	(2,598)
Principal payments received on real estate mortgage and other loans receivable	893
Escrow deposits for acquisitions of real estate	(1,000)	(1,000)
Net proceeds from the sale of real estate	13,004
Sale of other real estate investment		0
Distribution from subsidiary	0	0
Intercompany financing	44,216	56,527
Net cash used in investing activities	(27,675)	(167,799)
Cash flows from financing activities:
Proceeds from the issuance of common stock, net	0	0
Proceeds from the issuance of senior unsecured notes payable		300,000
Borrowings under unsecured revolving credit facility	60,000	158,000
Payments on senior unsecured notes payable		(267,639)
Payments on unsecured revolving credit facility	(135,000)	(158,000)
Payments of deferred financing costs		(6,047)
Net-settle adjustment on restricted stock	0	0
Dividends paid on common stock	0	0
Distribution to Parent	(45,827)	(38,544)
Intercompany financing	129,251	169,391
Net cash provided by financing activities	8,424	157,161
Net increase in cash and cash equivalents	8,836	7,308
Cash and cash equivalents, beginning of period	6,909	7,500
Cash and cash equivalents, end of period	15,745	14,808
Reportable Legal Entities | Combined Subsidiary Guarantors
Cash flows from operating activities:
Net cash (used in) provided by operating activities	44,310	49,144
Cash flows from investing activities:
Acquisitions of real estate	0	0
Improvements to real estate	(25)	(50)
Purchases of equipment, furniture and fixtures	(69)	(67)
Investment in real estate mortgage and other loans receivable	0
Principal payments received on real estate mortgage and other loans receivable	0
Escrow deposits for acquisitions of real estate	0	0
Net proceeds from the sale of real estate	0
Sale of other real estate investment		7,500
Distribution from subsidiary	0	0
Intercompany financing	0	0
Net cash used in investing activities	(94)	7,383
Cash flows from financing activities:
Proceeds from the issuance of common stock, net	0	0
Proceeds from the issuance of senior unsecured notes payable		0
Borrowings under unsecured revolving credit facility	0	0
Payments on senior unsecured notes payable		0
Payments on unsecured revolving credit facility	0	0
Payments of deferred financing costs		0
Net-settle adjustment on restricted stock	0	0
Dividends paid on common stock	0	0
Distribution to Parent	0	0
Intercompany financing	(44,216)	(56,527)
Net cash provided by financing activities	(44,216)	(56,527)
Net increase in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Elimination
Cash flows from operating activities:
Net cash (used in) provided by operating activities	0	0
Cash flows from investing activities:
Acquisitions of real estate	0	0
Improvements to real estate	0	0
Purchases of equipment, furniture and fixtures	0	0
Investment in real estate mortgage and other loans receivable	0
Principal payments received on real estate mortgage and other loans receivable	0
Escrow deposits for acquisitions of real estate	0	0
Net proceeds from the sale of real estate	0
Sale of other real estate investment		0
Distribution from subsidiary	(45,827)	(38,544)
Intercompany financing	85,035	112,864
Net cash used in investing activities	39,208	74,320
Cash flows from financing activities:
Proceeds from the issuance of common stock, net	0	0
Proceeds from the issuance of senior unsecured notes payable		0
Borrowings under unsecured revolving credit facility	0	0
Payments on senior unsecured notes payable		0
Payments on unsecured revolving credit facility	0	0
Payments of deferred financing costs		0
Net-settle adjustment on restricted stock	0	0
Dividends paid on common stock	0	0
Distribution to Parent	45,827	38,544
Intercompany financing	(85,035)	(112,864)
Net cash provided by financing activities	(39,208)	(74,320)
Net increase in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	$ 0	$ 0