Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Cash flows from operating activities:
Net income	$ 112,689	$ 102,160	$ 102,713	$ 95,430	$ 214,849	$ 198,143
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	54,406		51,892		109,065	103,641
Amortization of deferred financing costs					6,006	6,064
Non-cash interest expense related to amortization of discount on equity component of exchangeable senior notes					2,347	2,385
Compensation expense related to stock-based awards					6,952	5,842
Gain on real estate transactions					(1,205)	0
Distributions from unconsolidated real estate ventures in excess of earnings					3,334	3,615
Changes in operating assets and liabilities:
Other assets					1,890	7,269
Accounts payable and accrued expenses					21,632	7,888
Other liabilities					(1,463)	4,895
Net cash provided by operating activities					363,407	339,742
Cash flows from investing activities:
Acquisition of real estate assets					(248,808)	(238,153)
Development and redevelopment of real estate assets					(20,891)	(27,893)
Proceeds from sale of real estate assets, investments in real estate ventures and other assets					11,254	753
Investment in unconsolidated real estate ventures					(31,344)	(34,752)
Return of investment in unconsolidated real estate ventures					3,982	47,944
Issuance of notes receivable					(152,599)	0
Principal payments received from notes receivable					0	25,226
Purchase of equipment and fixtures					(2,023)	(2,220)
Net cash used in investing activities					(440,429)	(229,095)
Cash flows from financing activities:
Proceeds from the sale of common stock, net of offering costs					98,796	0
Proceeds from notes payable and revolving lines of credit					757,000	645,386
Principal payments on notes payable and revolving lines of credit					(524,370)	(487,016)
Principal payments on notes payable to trusts					(30,928)	0
Deferred financing costs					(587)	(3,028)
Repurchase of exchangeable senior notes					0	(58,469)
Net proceeds from exercise of stock options					2,227	1,170
Redemption of Operating Partnership units held by noncontrolling interests					0	(2,558)
Contributions from noncontrolling interests					50	120
Dividends paid on common stock					(225,095)	(206,813)
Distributions to noncontrolling interests					(17,117)	(16,377)
Net cash provided by (used in) financing activities					59,976	(127,585)
Net decrease in cash, cash equivalents, and restricted cash					(17,046)	(16,938)
Cash, cash equivalents, and restricted cash, beginning of the period		72,690		86,044	72,690	86,044	$ 86,044
Cash, cash equivalents, and restricted cash, end of the period	55,644		69,106		55,644	69,106	$ 72,690
Supplemental schedule of cash flow information
Interest paid					88,455	78,602
Income taxes paid					4,095	1,836
Redemption of Operating Partnership units held by noncontrolling interests for common stock
Common stock and paid-in capital					8,133	383
Establishment of operating lease right of use assets and lease liabilities
Real estate assets - operating lease right-of-use assets	129,511				225,017	0
Operating lease liabilities					(234,374)	0
Accounts payable and accrued expenses					9,357	0
Acquisitions of real estate assets
Real estate assets, net	8,424	223,740	237,284	70,787	232,164	308,071
Notes payable assumed	$ 0	$ (17,157)	$ (87,500)	$ 0	(17,157)	(87,500)
Accrued construction costs and capital expenditures
Acquisition of real estate assets					1,368	1,184
Development and redevelopment of real estate assets					0	1,558
Accounts payable and accrued expenses					(1,368)	(2,742)
Conversion of Preferred Operating Partnership Units to common Operating Partnership Units
Preferred Operating Partnership Units					4,374	0
Common Operating Partnership Units					(4,374)	0
Redemption of Operating Partnership units held by noncontrolling interests for common stock
Redemption of Operating Partnership units held by noncontrolling interests for common stock
Noncontrolling interests in Operating Partnership					(8,133)	(383)
Acquisitions of real estate assets
Acquisitions of real estate assets
Real estate assets, net					19,937	88,842
Value of Operating Partnership units issued					0	(1,877)
Notes payable assumed					(17,157)	(87,500)
Investment in unconsolidated real estate ventures					(2,780)	535
Contribution of Preferred Operating Partnership Units to unconsolidated real estate venture
Contribution of Preferred Operating Partnership Units to unconsolidated real estate venture
Investments in unconsolidated real estate ventures					(28,022)	0
Value of Preferred Operating Partnership units issued					$ 28,022	$ 0