Summarized Condensed Consolidating Information - Condensed Consolidating Statements of Cash Flows (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net cash (used in) provided by operating activities	$ 42,116	$ 44,901
Cash flows from investing activities:
Acquisitions of real estate	(47,310)	(96,641)
Improvements to real estate	(506)	(598)
Purchases of equipment, furniture and fixtures	(702)	(233)
Investment in real estate mortgage and other loans receivable	(1,390)	0
Principal payments received on mortgage loan receivable	58	0
Escrow deposits for acquisitions of real estate	(2,250)	(4,335)
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	(39,096)	(94,307)
Cash flows from financing activities:
Proceeds from the issuance of common stock, net	47,547	170,485
Proceeds from the issuance of senior unsecured notes payable	0	300,000
Borrowings under unsecured revolving credit facility	60,000	63,000
Payments on senior unsecured notes payable	0	(267,639)
Payments on unsecured revolving credit facility	(75,000)	(158,000)
Payments of deferred financing costs	0	(5,511)
Net-settle adjustment on restricted stock	(1,288)	(866)
Dividends paid on common stock	(29,628)	(24,497)
Distribution to Parent	0	0
Intercompany financing	0	0
Net cash provided by financing activities	1,631	76,972
Net increase in cash and cash equivalents	4,651	27,566
Cash and cash equivalents, beginning of period	6,909	7,500
Cash and cash equivalents, end of period	11,560	35,066
Reportable Legal Entities | Parent Guarantor
Cash flows from operating activities:
Net cash (used in) provided by operating activities	(7)	(141)
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 mortgage loan 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	29,628	24,497
Intercompany financing	(46,252)	(169,478)
Net cash used in investing activities	(16,624)	(144,981)
Cash flows from financing activities:
Proceeds from the issuance of common stock, net	47,547	170,485
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	(29,628)	(24,497)
Distribution to Parent	0	0
Intercompany financing	0	0
Net cash provided by financing activities	16,631	145,122
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	12,758	10,517
Cash flows from investing activities:
Acquisitions of real estate	(47,310)	(96,641)
Improvements to real estate	(495)	(556)
Purchases of equipment, furniture and fixtures	(645)	(169)
Investment in real estate mortgage and other loans receivable	(1,390)
Principal payments received on mortgage loan receivable	58
Escrow deposits for acquisitions of real estate	(2,250)	(4,335)
Net proceeds from the sale of real estate	13,004
Sale of other real estate investment		0
Distribution from subsidiary	0	0
Intercompany financing	29,297	41,919
Net cash used in investing activities	(9,731)	(59,782)
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	63,000
Payments on senior unsecured notes payable		(267,639)
Payments on unsecured revolving credit facility	(75,000)	(158,000)
Payments of deferred financing costs		(5,511)
Net-settle adjustment on restricted stock	0	0
Dividends paid on common stock	0	0
Distribution to Parent	(29,628)	(24,497)
Intercompany financing	46,252	169,478
Net cash provided by financing activities	1,624	76,831
Net increase in cash and cash equivalents	4,651	27,566
Cash and cash equivalents, beginning of period	6,909	7,500
Cash and cash equivalents, end of period	11,560	35,066
Reportable Legal Entities | Combined Subsidiary Guarantors
Cash flows from operating activities:
Net cash (used in) provided by operating activities	29,365	34,525
Cash flows from investing activities:
Acquisitions of real estate	0	0
Improvements to real estate	(11)	(42)
Purchases of equipment, furniture and fixtures	(57)	(64)
Investment in real estate mortgage and other loans receivable	0
Principal payments received on mortgage loan 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	(68)	7,394
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	(29,297)	(41,919)
Net cash provided by financing activities	(29,297)	(41,919)
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 mortgage loan 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	(29,628)	(24,497)
Intercompany financing	16,955	127,559
Net cash used in investing activities	(12,673)	103,062
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	29,628	24,497
Intercompany financing	(16,955)	(127,559)
Net cash provided by financing activities	12,673	(103,062)
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