Condensed Consolidated Statement of Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Distributions in Excess of Accumulated Earnings [Member]	Accumulated Other Comprehensive Loss, Net [Member]	Noncontrolling Interest [Member]
Balance at period beginning at Dec. 31, 2017	$ 6,396,825	$ 7	$ 7,129,571	$ (833,726)	$ (18,446)	$ 119,419
Balances (in shares) at Dec. 31, 2017		66,054,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	289,159			272,333		16,826
Reversal of unrealized gains upon the sale of marketable debt securities	6				6
Change in fair value of derivatives and amortization of swap settlements	12,630				12,210	420
Change in fair value of marketable debt securities, net	(87)				(84)	(3)
Issuance of common stock under:
Stock option and restricted stock plans, net	2,751		2,751
Stock option and restricted stock plans, net (in shares)		17,000
Sale of common stock, net	(483)		(483)
Equity based compensation costs	8,561		7,697			864
Retirement of common stock, net	(3,774)		(3,774)
Retirement of common stock, net (in shares)		(17,000)
Changes in the redemption value of redeemable noncontrolling interest	(2,253)		(2,032)			(221)
Distributions to noncontrolling interest	(22,281)					(22,281)
Redemptions of noncontrolling interest	(157)		(143)			(14)
Redemptions of noncontrolling interest (in shares)		1,000
Common stock dividends	(368,577)			(368,577)
Balance at period end at Sep. 30, 2018	6,436,028	$ 7	7,133,587	(808,085)	(8,548)	119,067
Balances (in shares) at Sep. 30, 2018		66,055,000
Balance at period beginning at Jun. 30, 2018	6,474,683	$ 7	7,131,809	(766,193)	(11,438)	120,498
Balances (in shares) at Jun. 30, 2018		66,050,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	86,110			80,975		5,135
Reversal of unrealized gains upon the sale of marketable debt securities	4				4
Change in fair value of derivatives and amortization of swap settlements	2,974				2,875	99
Change in fair value of marketable debt securities, net	12				11	1
Issuance of common stock under:
Stock option and restricted stock plans, net	887		887
Stock option and restricted stock plans, net (in shares)		5,000
Sale of common stock, net	(130)		(130)
Equity based compensation costs	1,747		1,496			251
Changes in the redemption value of redeemable noncontrolling interest	(408)		(386)			(22)
Distributions to noncontrolling interest	(6,884)					(6,884)
Redemptions of noncontrolling interest	(100)		(89)			(11)
Common stock dividends	(122,867)			(122,867)
Balance at period end at Sep. 30, 2018	6,436,028	$ 7	7,133,587	(808,085)	(8,548)	119,067
Balances (in shares) at Sep. 30, 2018		66,055,000
Issuance of common stock under:
Cumulative effect upon adoption of ASU No. 2017-12					175
Balance at period beginning at Dec. 31, 2018	6,393,844	$ 7	7,093,079	(812,796)	(13,217)	126,771
Balances (in shares) at Dec. 31, 2018		65,890,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	329,266			310,468		18,798
Reversal of unrealized gains upon the sale of marketable debt securities	(32)				(31)	(1)
Change in fair value of derivatives and amortization of swap settlements	(6,366)				(6,152)	(214)
Change in fair value of marketable debt securities, net	203				197	6
Issuance of common stock under:
Stock option and restricted stock plans, net	32,907		32,907
Stock option and restricted stock plans, net (in shares)		188,000
Sale of common stock, net	72,549	$ 73,400	72,549
Sale of common stock, net (in shares)		228,271
Equity based compensation costs	7,914		7,016			898
Retirement of common stock, net	(56,989)		(56,989)
Retirement of common stock, net (in shares)		(234,000)
Changes in the redemption value of redeemable noncontrolling interest	(3,675)		(5,048)			1,373
Changes in noncontrolling interest from acquisition	65,472					65,472
Distributions to noncontrolling interest	(20,897)					(20,897)
Redemptions of noncontrolling interest	(14,180)		(11,872)			(2,308)
Redemptions of noncontrolling interest (in shares)		10,000
Common stock dividends	(385,193)			(385,193)
Balance at period end at Sep. 30, 2019	6,415,004	$ 7	7,131,642	(887,521)	(19,028)	189,904
Balances (in shares) at Sep. 30, 2019		66,082,000
Balance at period beginning at Jun. 30, 2019	6,345,116	$ 7	7,031,886	(857,994)	(18,992)	190,209
Balances (in shares) at Jun. 30, 2019		65,727,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	105,700			99,335		6,365
Change in fair value of derivatives and amortization of swap settlements	(12)				(12)	0
Change in fair value of marketable debt securities, net	(25)				(24)	(1)
Issuance of common stock under:
Stock option and restricted stock plans, net	27,679		27,679
Stock option and restricted stock plans, net (in shares)		126,000
Sale of common stock, net	72,631		72,631
Sale of common stock, net (in shares)		228,000
Equity based compensation costs	1,814		1,544			270
Changes in the redemption value of redeemable noncontrolling interest	(2,247)		(2,309)			62
Distributions to noncontrolling interest	(6,789)					(6,789)
Redemptions of noncontrolling interest	(1)		211			(212)
Redemptions of noncontrolling interest (in shares)		1,000
Common stock dividends	(128,862)			(128,862)
Balance at period end at Sep. 30, 2019	$ 6,415,004	$ 7	$ 7,131,642	$ (887,521)	$ (19,028)	$ 189,904
Balances (in shares) at Sep. 30, 2019		66,082,000