Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income (Loss)	Cumulative Net Income	Cumulative Dividends	Total Stockholders' Equity	Non-controlling Interests
Beginning Balance at Dec. 31, 2012	$ 1,120,944	$ 0	$ 875	$ 2,100,297	$ (2,092)	$ 801,416	$ (1,779,552)	$ 1,120,944
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs	220,259		83	220,176				220,259
Common stock redemption	(454)			(454)				(454)
Stock-based compensation	5,210		1	5,209				5,210
Net income	6,983					6,946		6,946	$ 37
Amounts reclassified from accumulated other comprehensive loss arising from loss on defined benefit pension plan	2,143				2,143			2,143
Dividends to common stockholders ($1.20 per share)	(111,571)						(111,571)	(111,571)
Distributions to noncontrolling interests	(34)								(34)
Proceeds from noncontrolling interest	1,806								1,806
Ending Balance at Dec. 31, 2013	1,245,286	0	959	2,325,228	51	808,362	(1,891,123)	1,243,477	1,809
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs	76,831		31	76,800				76,831
Common stock redemption	(10,074)		(4)	(10,070)				(10,074)
Stock-based compensation	4,451		2	4,449				4,451
Net income	32,200					31,887		31,887	313
Amounts reclassified from accumulated other comprehensive loss arising from loss on defined benefit pension plan	(2,570)				(2,570)			(2,570)
Dividends to common stockholders ($1.20 per share)	(116,371)						(116,371)	(116,371)
Distributions to noncontrolling interests	(510)								(510)
Purchase of noncontrolling interest in consolidated joint ventures	(8,189)			(6,577)				(6,577)	(1,612)
Ending Balance at Dec. 31, 2014	1,221,054	0	988	2,389,830	(2,519)	840,249	(2,007,494)	1,221,054
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs	66,911		25	66,886				66,911
Common stock redemption	(1,367)			(1,367)				(1,367)
Stock-based compensation	6,029		2	6,027				6,029
Net income	69,436					69,436		69,436
Amounts reclassified from accumulated other comprehensive loss arising from loss on defined benefit pension plan	2,519				2,519			2,519
Loss on forward starting interest rate swaps	(1,569)	0	0	0	(1,569)	0	0	(1,569)	$ 0
Dividends to common stockholders ($1.20 per share)	(120,266)						(120,266)	(120,266)
Ending Balance at Dec. 31, 2015	$ 1,242,747	$ 0	$ 1,015	$ 2,461,376	$ (1,569)	$ 909,685	$ (2,127,760)	$ 1,242,747