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, 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
Increase (Decrease) in Stockholders' Equity
Net income	46,402							46,402		0
Unrealized gain (loss) on derivative instrument	673								673
Unrealized loss on marketable securities	0
Purchase of shares (in shares)					(983,789)
Purchase of shares	(25,563)				$ (10)		(25,553)
Share-based compensation (in shares)					136,623
Share-based compensation	4,353				$ 2		4,351			0
Distributions	(6,981)			(6,981)
Balance (in shares) at Mar. 31, 2016		4,915,196	11,000,000		125,502,748
Balance at Mar. 31, 2016	$ 3,387,371	$ 119,263	$ 265,391	(657,176)	$ 1,255	(3,111,868)	4,393,409	2,380,111	(3,014)	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
Increase (Decrease) in Stockholders' Equity
Net income	23,822							23,814		8
Unrealized gain (loss) on derivative instrument	(153)								(153)
Unrealized loss on marketable securities	(641)								(641)
Purchase of shares (in shares)					(6,694)
Purchase of shares	(209)				$ 0		(209)
Share-based compensation (in shares)					76,424
Share-based compensation	5,226				$ 0		4,999			227
Contributions	30									30
Distributions	$ (1,997)			(1,997)
Adjustment for noncontrolling interest							(777)			777
Balance (in shares) at Mar. 31, 2017	124,064,195	4,915,196	0		124,064,195
Balance at Mar. 31, 2017	$ 3,286,525	$ 119,263	$ 0	$ (679,757)	$ 1,240	$ (3,111,868)	$ 4,367,190	$ 2,590,417	$ (1,002)	$ 1,042