CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Series D	Series E	Cumulative Preferred Distributions	Common Shares	Cumulative Common Distributions	Additional Paid in Capital	Cumulative Net Income	Cumulative Other Comprehensive Loss	Noncontrolling Interest
Balance (in shares) at Dec. 31, 2014		4,915,497	11,000,000		129,607,279
Balance at Dec. 31, 2014	$ 3,319,583	$ 119,266	$ 265,391	$ (622,271)	$ 1,296	$ (3,111,868)	$ 4,487,133	$ 2,233,852	$ (53,216)	$ 0
Comprehensive income:
Net income	99,857							99,857		0
Unrealized gain (loss) on derivative instrument	612								612
Unrealized gain on marketable securities	0
Foreign currency translation adjustments	48,917								48,917
Total comprehensive income	149,386
Purchase of shares	(87,983)				$ (35)		(87,948)			0
Purchase of shares (in shares)					(3,410,300)
Redemption of shares (in shares)		(301)			144
Redemption of shares	0	$ (3)		0	$ 0		3
Excess fair value of consideration paid over carrying value of preferred shares	0
Share-based compensation (in shares)					152,791
Share-based compensation	15,425				$ 2		15,423			0
Distributions	(27,924)			(27,924)		0
Distributions										0
Balance (in shares) at Dec. 31, 2015		4,915,196	11,000,000		126,349,914
Balance at Dec. 31, 2015	3,368,487	$ 119,263	$ 265,391	(650,195)	$ 1,263	(3,111,868)	4,414,611	2,333,709	(3,687)	0
Comprehensive income:
Net income	232,894							232,894		0
Unrealized gain (loss) on derivative instrument	3,479								3,479
Unrealized gain on marketable securities	0
Foreign currency translation adjustments	0
Total comprehensive income	236,373
Purchase of shares	(69,987)				$ (25)		(69,962)			0
Purchase of shares (in shares)					(2,491,675)
Redemption of shares (in shares)		0	(11,000,000)		0
Redemption of shares	(275,000)	$ 0	$ (275,000)	0	$ 0		0
Excess fair value of consideration paid over carrying value of preferred shares	(9,609)		$ 9,609	(9,609)
Share-based compensation (in shares)					136,226
Share-based compensation	18,530				$ 2		18,528			0
Distributions	$ (17,956)			(17,956)		0
Distributions										0
Balance (in shares) at Dec. 31, 2016	123,994,465	4,915,196	0		123,994,465
Balance at Dec. 31, 2016	$ 3,260,447	$ 119,263	$ 0	(677,760)	$ 1,240	(3,111,868)	4,363,177	2,566,603	(208)	0
Comprehensive income:
Net income	29,666							29,656		10
Unrealized gain (loss) on derivative instrument	(248)								(248)
Unrealized gain on marketable securities	361								361
Foreign currency translation adjustments	0
Total comprehensive income	29,779
Purchase of shares	(3,188)				$ 0		(3,188)
Purchase of shares (in shares)					(43,329)
Excess fair value of consideration paid over carrying value of preferred shares	0
Share-based compensation (in shares)					266,480
Share-based compensation	21,414				$ 2		20,156			1,256
Contributions	31									31
Distributions	(7,988)			(7,988)		0
Distributions										0
Adjustment for noncontrolling interest	$ 0						168			(168)
Balance (in shares) at Dec. 31, 2017	124,217,616	4,915,196	0		124,217,616
Balance at Dec. 31, 2017	$ 3,300,495	$ 119,263	$ 0	$ (685,748)	$ 1,242	$ (3,111,868)	$ 4,380,313	$ 2,596,259	$ (95)	$ 1,129