CONSOLIDATED STATEMENTS OF EQUITY - USD ($) shares in Thousands, $ in Thousands	Total Shareholders' Equity	Common Shares	Preferred Shares	Additional Paid-in Capital	Accumulated Other Comprehensive (Loss) Income	Accumulated Deficit	Noncontrolling Interest in Subsidiaries	Noncontrolling Interests in Operating Partnership	Total
Balance at Dec. 31, 2014	$ 1,448,026	$ 1,639	$ 31	$ 1,974,308	$ (8,759)	$ (519,193)	$ 1,592		$ 1,449,618
Balance (in shares) at Dec. 31, 2014		163,957	3,100
Balance of Noncontrolling Interests in the Operating Partnership at Dec. 31, 2014								$ 49,823
Increase (Decrease) in Stockholders' Equity
Contributions from noncontrolling interests in subsidiaries							178		178
Issuance of common shares, net	29,441	$ 12		29,429					29,441
Issuance of common shares, net (in shares)		1,210
Issuance of restricted shares	1	$ 1							1
Issuance of restricted shares (in shares)		126
Conversion from units to shares	74			74				(74)	74
Conversion from units to shares (in shares)		3
Exercise of stock options	8,438	$ 9		8,429					8,438
Exercise of stock options (in shares)		855
Amortization of restricted shares	(789)			(789)					(789)
Share compensation expense	244			244					244
Adjustment for noncontrolling interest in the Operating Partnership	(4,982)					(4,982)		4,982	(4,982)
Net income (loss)	8,434					8,434	(3)		8,431
Net income (loss)								91
Other comprehensive income (loss), net	(1,076)				(1,076)		(10)		(1,086)
Other comprehensive income (loss), net								(15)
Preferred share distributions	(1,502)					(1,502)			(1,502)
Common share distributions	(26,617)					(26,617)		(361)	(26,617)
Balance at Mar. 31, 2015	1,459,692	$ 1,661	$ 31	2,011,695	(9,835)	(543,860)	1,757		1,461,449
Balance (in shares) at Mar. 31, 2015		166,151	3,100
Balance of Noncontrolling Interests in the Operating Partnership at Mar. 31, 2015								54,446
Balance at Dec. 31, 2014	1,448,026	$ 1,639	$ 31	1,974,308	(8,759)	(519,193)	1,592		1,449,618
Balance (in shares) at Dec. 31, 2014		163,957	3,100
Balance of Noncontrolling Interests in the Operating Partnership at Dec. 31, 2014								49,823
Balance at Dec. 31, 2015	1,643,327	$ 1,747	$ 31	2,231,181	(4,978)	(584,654)	1,526		1,644,853
Balance (in shares) at Dec. 31, 2015		174,668	3,100
Balance of Noncontrolling Interests in the Operating Partnership at Dec. 31, 2015								66,128	66,128
Increase (Decrease) in Stockholders' Equity
Issuance of common shares, net	62,890	$ 20		62,870					62,890
Issuance of common shares, net (in shares)		2,023
Issuance of restricted shares	1	$ 1							1
Issuance of restricted shares (in shares)		106
Exercise of stock options	5,887	$ 3		5,884					5,887
Exercise of stock options (in shares)		330
Amortization of restricted shares	(712)			(712)					(712)
Share compensation expense	304			304					304
Adjustment for noncontrolling interest in the Operating Partnership	(6,073)					(6,073)		6,073	(6,073)
Net income (loss)	15,750					15,750	(67)		15,683
Net income (loss)								172
Other comprehensive income (loss), net	(324)				(324)				(324)
Other comprehensive income (loss), net								(4)
Preferred share distributions	(1,502)					(1,502)			(1,502)
Common share distributions	(37,255)					(37,255)		(453)	(37,255)
Balance at Mar. 31, 2016	$ 1,682,293	$ 1,771	$ 31	$ 2,299,527	$ (5,302)	$ (613,734)	$ 1,459		1,683,752
Balance (in shares) at Mar. 31, 2016		177,127	3,100
Balance of Noncontrolling Interests in the Operating Partnership at Mar. 31, 2016								$ 71,916	$ 71,916