Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 21,839	$ 130	$ 23,276	$ 2,521
Adjustment to reconcile net income to net cash provided by operating activities:
Depreciation and amortization			110,286	91,725
Loss on impairments	0	0	0	11,231
Loss on involuntary conversion			330	0
Non-cash portion of interest expense			1,465	1,208
Intangible amortization in rental income, net			3,873	4,751
Straight-line rent adjustments, net			(4,855)	(2,205)
Dividends on forfeited equity compensation			2	3
Loss on extinguishment of debt	13	0	15	1,973
Gain on the sales of rental property, net			(19,225)	(21,589)
Non-cash compensation expense			7,159	7,692
Change in assets and liabilities:
Tenant accounts receivable, net			(955)	(215)
Restricted cash			483	(461)
Prepaid expenses and other assets			(10,479)	(7,375)
Accounts payable, accrued expenses and other liabilities			5,572	8,128
Tenant prepaid rent and security deposits			3,570	518
Total adjustments			97,241	95,384
Net cash provided by operating activities			120,517	97,905
Cash flows from investing activities:
Acquisitions of land and buildings and improvements			(405,790)	(195,893)
Additions of land and building and improvements			(27,539)	(20,703)
Proceeds from sales of rental property, net			43,454	50,301
Proceeds from insurance on involuntary conversion			857	0
Restricted cash			5,583	(469)
Acquisition deposits, net			685	(1,315)
Acquisitions of deferred leasing intangibles			(79,961)	(51,937)
Net cash used in investing activities			(462,711)	(220,016)
Cash flows from financing activities:
Proceeds from sale of series C preferred stock			0	75,000
Proceeds from unsecured credit facility			538,000	286,000
Repayment of unsecured credit facility			(321,000)	(213,000)
Repayment of mortgage notes			(105,027)	(33,084)
Payment of loan fees and costs			(1,170)	(140)
Payment of loan prepayment fees and costs			(15)	(1,969)
Dividends and distributions			103,655	86,890
Proceeds from sales of common stock			339,624	100,714
Repurchase and retirement of restricted stock			(969)	0
Offering costs			(4,746)	(4,258)
Net cash provided by financing activities			341,042	122,373
Increase (decrease) in cash and cash equivalents			(1,152)	262
Cash and cash equivalents—beginning of period			12,192	12,011	$ 12,011
Cash and cash equivalents—end of period	11,040	12,273	11,040	12,273	12,192
Supplemental disclosure:
Cash paid for interest, net of capitalized interest			30,476	29,127
Supplemental schedule of non-cash investing and financing activities
Issuance of units for acquisitions of land and building and improvements and deferred leasing intangibles			18,558	0
Acquisitions of land and buildings and improvements			17,304	3,392
Acquisitions of deferred leasing intangibles			(2,064)	(938)
Partial disposal of building due to involuntary conversion of building			363	492
Investing other receivables due to involuntary conversion of building			(363)	(492)
Change in additions of land, building, and improvements included in accounts payable, accrued expenses, and other liabilities			(13,201)	(1,587)
Additions to building and other capital improvements from non-cash compensation			(24)	(14)
Assumption of mortgage notes			0	4,037
Fair market value adjustment to mortgage notes acquired			0	75
Change in loan fees, costs, and offering costs included in accounts payable, accrued expenses, and other liabilities			30	6
Dividends and distributions payable	$ 11,516	$ 8,814	$ 11,516	$ 8,814	$ 9,728