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
Balance at Dec. 31, 2013	$ 3,363,586	$ 368,270	$ 265,391	$ (573,971)	$ 1,184	$ (3,082,271)	$ 4,213,474	$ 2,209,840	$ (38,331)
Balance (in shares) at Dec. 31, 2013		15,180,000	11,000,000		118,386,918
Comprehensive income (loss):
Net income	24,012							24,012
Unrealized gain on derivative instrument	7,407								7,407
Foreign currency translation adjustments	(22,270)								(22,270)
Equity in unrealized loss of an investee	(22)								(22)
Total comprehensive income	9,127
Issuance of shares, net	2,402				$ 0		2,402
Issuance of shares, net (in shares)					90,135
Redemption of shares	0	$ (249,004)		(16,205)	$ 104		265,105
Redemption of shares (in shares)		(10,264,503)			10,412,499
Excess fair value of consideration paid over carrying value of preferred shares	0
Share grants	6,160				$ 8		6,152
Share grants (in shares)					717,727
Distributions	(61,692)			(32,095)		(29,597)
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)
Balance (in shares) at Dec. 31, 2014		4,915,497	11,000,000		129,607,279
Comprehensive income (loss):
Net income	99,857							99,857
Unrealized gain on derivative instrument	612								612
Foreign currency translation adjustments	48,917								48,917
Equity in unrealized loss of an investee	0
Total comprehensive income	149,386
Redemption of shares	0	$ (3)		0	$ 0		3
Redemption of shares (in shares)		(301)			144
Excess fair value of consideration paid over carrying value of preferred shares	0
Share grants	15,425				$ 2		15,423
Share grants (in shares)					152,791
Purchase of shares	(87,983)				$ (35)		(87,948)
Purchase of shares (in shares)					(3,410,300)
Distributions	(27,924)			(27,924)		0
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)
Balance (in shares) at Dec. 31, 2015	126,349,914	4,915,196	11,000,000		126,349,914
Comprehensive income (loss):
Net income	$ 232,894							232,894
Unrealized gain on derivative instrument	3,479								3,479
Foreign currency translation adjustments	0
Equity in unrealized loss of an investee	0
Total comprehensive income	236,373
Redemption of shares	(275,000)	$ 0	$ (275,000)	0	$ 0		0
Redemption of shares (in shares)		0	(11,000,000)		0
Excess fair value of consideration paid over carrying value of preferred shares	(9,609)		$ 9,609	(9,609)
Share grants	18,530				$ 2		18,528
Share grants (in shares)					136,226
Purchase of shares	(69,987)				$ (25)		(69,962)
Purchase of shares (in shares)					(2,491,675)
Distributions	(17,956)			(17,956)		0
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)
Balance (in shares) at Dec. 31, 2016	123,994,465	4,915,196	0		123,994,465