Consolidated Statements of Stockholders' Equity (USD $) In Thousands, unless otherwise specified	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Loss	Cumulative Net Income	Cumulative Dividends	Total Stockholders' Equity	Non-controlling Interests
Beginning Balance at Dec. 31, 2009	$ 790,148		$ 606	$ 1,520,893	$ (4,593)	$ 787,965	$ (1,518,105)	$ 786,766	$ 3,382
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs	118,130		53	118,077				118,130
Stock-based compensation	2,411		2	2,409				2,411
Net income (loss)	8,247					8,200		8,200	47
Defined benefit pension plan net gain (loss)	(676)				(676)			(676)
Dividends to common stockholders ($1.20 per share)	(75,821)						(75,821)	(75,821)
Distributions to noncontrolling interests	(467)								(467)
Proceeds from noncontrolling interests	768								768
Ending Balance at Dec. 31, 2010	842,740		661	1,641,379	(5,269)	796,165	(1,593,926)	839,010	3,730
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs	251,976		117	251,859				251,976
Common stock redemption	(86)			(86)				(86)
Stock-based compensation	2,922		1	2,921				2,922
Net income (loss)	(184)					(214)		(214)	30
Defined benefit pension plan net gain (loss)	1,937				1,937			1,937
Dividends to common stockholders ($1.20 per share)	(89,270)						(89,270)	(89,270)
Distributions to noncontrolling interests	(249)								(249)
Proceeds from noncontrolling interests	76								76
Purchase of noncontrolling interest in consolidated joint ventures	(5,056)			(1,469)				(1,469)	(3,587)
Ending Balance at Dec. 31, 2011	1,004,806		779	1,894,604	(3,332)	795,951	(1,683,196)	1,004,806
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs	202,365		93	202,272				202,365
Common stock redemption	(68)			(68)				(68)
Stock-based compensation	3,492		3	3,489				3,492
Net income (loss)	5,535					5,465		5,465	70
Defined benefit pension plan net gain (loss)	1,240				1,240			1,240
Dividends to common stockholders ($1.20 per share)	(96,356)						(96,356)	(96,356)
Distributions to noncontrolling interests	(70)								(70)
Ending Balance at Dec. 31, 2012	$ 1,120,944		$ 875	$ 2,100,297	$ (2,092)	$ 801,416	$ (1,779,552)	$ 1,120,944