Consolidated Statements of Stockholders' Equity (USD $) In Thousands, unless otherwise specified	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, 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	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 interest	76								76
Purchase of noncontrolling interest in consolidated joint ventures	(5,056)	0	0	(1,469)	0	0	0	(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	1,240				1,240			1,240
Dividends to common stockholders ($1.20 per share)	(96,356)						(96,356)	(96,356)
Proceeds from noncontrolling interest	(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
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 (loss)	6,983					6,946		6,946	37
Defined benefit pension plan net gain	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		$ 959	$ 2,325,228	$ 51	$ 808,362	$ (1,891,123)	$ 1,243,477	$ 1,809