Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018	Dec. 31, 2017
Operating activities:
Net income	$ 202,243		$ 266,983	$ 262,968
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Gain on Extinguishment of Debt	0		0	(977)
asset impairment charges cont and discops	23,639		27,283	10,195
Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property	36,053		3,037	41,942
Gain on insurance recovery	0		0	(606)
Deferred income tax benefit (expense)	(4,115)		573	812
gain on sale of investment in direct financing lease	0		5,514	0
write off of deferred debt issuance cost cont and disc	38,450		31,958	1,549
Equity in loss (income) from joint ventures	381		22	(72)
Distributions from joint ventures	112		567	442
depreciation and amort cont and discops	171,763		153,430	132,946
Amortization of deferred financing costs	6,192		5,797	6,167
Amortization of above/below market leases and tenant allowances, net	(343)		(581)	(107)
Share-based compensation expense to management and trustees	13,180		15,111	14,142
Share-based compensation expense included in severance expense	580		3,218	0
Increase (Decrease) in Operating Lease Assets and Liabilities, Net	1,194		0	0
Mortgage notes accrued interest receivable	(381)		(517)	467
Accounts receivable	(1,385)		(22,300)	8,866
Increase in direct financing lease receivable	(186)		(563)	(1,208)
Other assets	(1,301)		(1,055)	(1,691)
Accounts payable and accrued liabilities	27,540		4,979	260
Increase (Decrease) in Deferred Revenue	(1,980)		7,974	6,061
Net cash provided by operating activities	439,530		484,328	398,272
Investing activities:
Acquisition of rental properties and other assets	(500,629)		(187,460)	(397,556)
Proceeds from Sale of Real Estate	216,020		22,134	191,569
Proceeds from sale of public charter school portfolio	449,555		0	0
Investment in unconsolidated joint ventures	325		29,473	0
Proceeds from settlement of derivative	0		(30,796)	0
Investment in mortgage notes receivable	(142,456)		(36,105)	(133,697)
Proceeds from mortgage note receivable paydown	217,459		335,168	21,784
Investment in promissory notes receivable	12,271		7,863	1,928
Proceeds from promissory note receivable paydown	3,738		7,500	1,599
Proceeds from insurance recovery	0		0	606
Proceeds from Sale of Lease Receivables	0		43,447	0
Additions to properties under development	(134,586)		(274,956)	(384,449)
Net cash provided (used) by investing activities	96,505		(96,812)	(702,072)
Financing activities:
Proceeds from Issuance of Long-term Debt	962,000		908,000	1,371,000
Principal payments on long-term debt	(866,735)		(949,684)	(823,288)
Deferred financing fees paid	(9,386)		(8,642)	(14,318)
Costs associated with loan refinancing or payoff (cash portion)	(36,918)		(28,650)	(7)
Net proceeds from issuance of common shares	305,556		956	99,069
Proceeds from Issuance of Preferred Stock and Preference Stock	0		0	144,490
Payments for Repurchase of Redeemable Preferred Stock	0		0	125,025
Payment, Tax Withholding, Share-based Payment Arrangement	(732)		(62)	(5)
Purchase of common shares for treasury	(9,691)		(7,156)	(6,729)
Dividends paid to shareholders	(367,317)		(342,315)	(311,721)
Net cash (used) provided by financing activities	(23,223)		(427,553)	333,466
Effect of exchange rate changes on cash	121		(442)	241
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	531,440		18,507	58,986
Restricted Cash and Cash Equivalents	2,677		12,635	17,069
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	512,933		(40,479)	29,907
Cash and cash equivalents at beginning of the year	5,872		41,917	19,335
Cash and cash equivalents at end of the year	528,763		5,872	41,917
Supplemental schedule of non-cash activity:
Transfer of property under development to rental property	354,568		228,572	408,593
Issuance of nonvested shares and restricted share units at fair value, including nonvested shares issued for payment of bonuses	17,590		18,252	24,062
Noncash or Part Noncash Acquisition, Value of Assets Acquired	0		155,185	9,237
Conversion of rental property to mortgage note receivable	27,423		0	11,897
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	229,620		0	0
Operating Lease, Cost	253,486		0	0
Straight-Line Rent Receivable	73,382	[1]	73,332
Other Real Estate, Additions	14,000		0	0
Noncash or Part Noncash Acquisition, Debt Assumed	18,585		0	0
Stock Issued During Period, Value, Acquisitions	0		0	657,473
Assumption of liabilities net of accounts receivable for acquisition	0		0	12,083
Transfer of investment in a direct financing lease to rental properties	0		0	35,807
Supplemental disclosure of cash flow information:
Interest Paid, Excluding Capitalized Interest, Operating Activities	143,530		145,559	136,345
Cash paid during the year for income taxes	1,842		1,363	1,499
Interest cost capitalized	5,326		9,903	9,879
Change in accrued capital expenditures	(35,155)		32,993	333
Ground Lease Arrangement [Member]
Supplemental schedule of non-cash activity:
Straight-Line Rent Receivable	$ 24,454		$ 0	$ 0

[1] (1) At December 31, 2019, includes $24.6 million in sub-lessor straight-line rent receivables. Sub-lessor straight-line receivables relate to the Company's operating ground leases. The Company's tenants, who are generally sub-tenants under these ground leases, are responsible for paying the rent under these leases. See Note 16 for information related to the Company's leases.