CONDENSED CONSOLIDATED STATEMENT OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Preferred Shares	Common Stock	Additional Paid-in-Capital	Accumulated Distributions in Excess of Net Income	Accumulated Other Comprehensive Income (Loss)	Non-controlling Interests
Beginning Balance at Dec. 31, 2017	$ 1,340,835	$ 94,016	$ 24	$ 2,818,520	$ (1,589,724)	$ 1,065	$ 16,934
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemption of noncontrolling OP units for common shares	0			63			(63)
Issuance of common shares and deferred compensation amortization, net	5,016			5,016
Repurchase of common shares	(17,387)			(17,387)
Repurchase of common shares to settle tax obligations	(2,544)			(2,544)
Forfeiture of employee common shares	(71)			(87)	16
Dividends/distributions	(133,667)				(130,968)		(2,699)
Net income	205,232				202,007		3,225
Unrealized loss included in other comprehensive income	(413)					(413)
Ending Balance at Sep. 30, 2018	1,397,001	94,016	24	2,803,581	(1,518,669)	652	17,397
Beginning Balance at Jun. 30, 2018	1,229,296	94,016	24	2,811,981	(1,693,165)	1,098	15,342
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common shares and deferred compensation amortization, net	1,625			1,625
Repurchase of common shares	(10,025)			(10,025)
Forfeiture of employee common shares	7				7
Dividends/distributions	(44,306)				(43,527)		(779)
Net income	220,850				218,016		2,834
Unrealized loss included in other comprehensive income	(446)					(446)
Ending Balance at Sep. 30, 2018	1,397,001	94,016	24	2,803,581	(1,518,669)	652	17,397
Beginning Balance at Dec. 31, 2018	1,346,678	94,016	24	2,772,855	(1,537,100)	76	16,807
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemption of noncontrolling OP units for common shares	0			504			(504)
Issuance of common shares and deferred compensation amortization, net	136,585		2	136,583
Repurchase of common shares	(958)			(958)
Repurchase of common shares to settle tax obligations	(5,281)		(1)	(5,280)
Forfeiture of employee common shares	15			0	15
Dividends/distributions	(80,249)				(78,053)		(2,196)
Net income	199,870				194,679		5,191
Unrealized loss included in other comprehensive income	(5,625)					(5,625)
Ending Balance at Sep. 30, 2019	1,591,035	94,016	25	2,903,704	(1,420,459)	(5,549)	19,298
Beginning Balance at Jun. 30, 2019	1,344,174	94,016	23	2,771,213	(1,536,752)	0	15,674
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Redemption of noncontrolling OP units for common shares				343			(343)
Issuance of common shares and deferred compensation amortization, net	133,489		2	133,487
Repurchase of common shares to settle tax obligations	(1,339)			(1,339)
Forfeiture of employee common shares	10			0	10
Dividends/distributions	(27,571)				(27,036)		(535)
Net income	147,821				143,319		4,502
Unrealized loss included in other comprehensive income	(5,549)					(5,549)
Ending Balance at Sep. 30, 2019	$ 1,591,035	$ 94,016	$ 25	$ 2,903,704	$ (1,420,459)	$ (5,549)	$ 19,298