CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 316,477	$ 284,855	$ 271,940
Adjustments to net income:
Depreciation and amortization	449,943	409,215	374,661
Income from discontinued operations			(2,800)
Amortization of share-based compensation	12,007	10,391	11,959
Non-cash rental adjustments	(10,154)	(8,607)	(6,848)
Amortization of net premiums on mortgages payable	(3,414)	(7,482)	(12,891)
Amortization of deferred financing costs	8,904	9,044	8,335
(Gain) loss on interest rate swaps	(1,639)	3,043	1,349
Gain on sales of real estate	(21,979)	(22,243)	(39,205)
Provisions for impairment on real estate	20,664	10,560	4,126
Change in assets and liabilities
Accounts receivable and other assets	(1,232)	(2,641)	(3,064)
Accounts payable, accrued expenses and other liabilities	34,468	6,168	20,130
Net cash provided by operating activities	804,045	692,303	627,692
CASH FLOWS FROM INVESTING ACTIVITIES
Investment in real estate	(1,798,892)	(1,266,885)	(1,228,243)
Improvements to real estate, including leasing costs	(13,426)	(11,541)	(6,032)
Proceeds from sales of real estate:
Continuing operations	99,096	65,817	88,688
Discontinued operations			6,918
Collection of loans receivable	12,515		350
Restricted escrow deposits for Section 1031 tax-deferred exchanges and pending acquisitions	(404)	33,554	(36,540)
Net cash used in investing activities	(1,701,111)	(1,179,055)	(1,174,859)
CASH FLOWS FROM FINANCING ACTIVITIES
Cash distributions to common stockholders	(610,516)	(533,238)	(479,256)
Cash dividends to preferred stockholders	(27,080)	(27,080)	(38,300)
Borrowings on line of credit	3,879,000	1,448,000	1,672,321
Payments on line of credit	(2,997,000)	(1,433,000)	(1,577,321)
Proceeds from notes and bonds payable issued	592,026		598,594
Principal payments on notes payable	(275,000)	(150,000)
Proceeds from mortgages payable	9,963
Principal payments on mortgages payable	(231,743)	(198,353)	(85,208)
Proceeds from term loans		250,000
Proceeds from common stock offerings, net	383,572	793,559	528,615
Proceeds from dividend reinvestment and stock purchase plan	10,252	363,029	158,462
Procceds from At-the-Market (ATM) program	166,781	36,348
Redemption of preferred stock			(220,000)
Redemption of preferred units		(6,750)
Redemption of common units	(9,026)
Distributions to noncontrolling interests	(12,725)	(1,679)	(1,844)
Debt issuance costs	(5,274)	(10,259)	(5,505)
Other items, including shares withheld upon vesting	(7,038)	(7,383)	(9,796)
Net cash provided by financing activities	866,192	523,194	540,762
Net (decrease) increase in cash and cash equivalents	(30,874)	36,442	(6,405)
Cash and cash equivalents, beginning of period	40,294	3,852	10,257
Cash and cash equivalents, end of period	$ 9,420	$ 40,294	$ 3,852