Consolidated Statements Of Changes In Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income	Cumulative Earnings	Cumulative Distributions to Stockholders	Noncontrolling Interest
Beginning balance at Dec. 31, 2010	$ 1,075,592	$ 781	$ 1,689,851	$ 112,339	$ 474,940	$ (1,213,158)	$ 10,839
Beginning balance (in shares) at Dec. 31, 2010		78,124,668
Net income	25,196				26,343		(1,147)
Other comprehensive (loss) income	(121,326)			(125,490)			4,164
Issuance of common stock:
Dividend reinvestment & stock purchase plans (in shares)		708,664
Dividend reinvestment & stock purchase plans	8,791	7	8,784
Employee stock purchase and incentive plans (in shares)		374,662
Employee stock purchase and incentive plans	(2,778)	4	(2,782)
Non-cash equity award compensation	9,108		9,108
Share repurchases (in shares)		(652,086)
Share repurchases	(6,988)	(6)	(6,982)
Distributions to noncontrolling interest, net	(14,112)						(14,112)
Common dividends declared	(81,155)					(81,155)
Deconsolidation elimination	256						256
Ending balance at Dec. 31, 2011	892,584	786	1,697,979	(13,151)	501,283	(1,294,313)
Ending balance (in shares) at Dec. 31, 2011		78,555,908
Net income	131,769				131,769
Other comprehensive (loss) income	151,483			151,483
Issuance of common stock:
Dividend reinvestment & stock purchase plans (in shares)		2,741,168
Dividend reinvestment & stock purchase plans	38,580	28	38,552
Employee stock purchase and incentive plans (in shares)		419,340
Employee stock purchase and incentive plans	(1,816)	3	(1,819)
Non-cash equity award compensation	9,842		9,842
Common dividends declared	(82,278)					(82,278)
Ending balance at Dec. 31, 2012	1,140,164	817	1,744,554	138,332	633,052	(1,376,591)
Ending balance (in shares) at Dec. 31, 2012		81,716,416
Net income	173,246				173,246
Other comprehensive (loss) income	10,434			10,434
Issuance of common stock:
Dividend reinvestment & stock purchase plans (in shares)		431,679
Dividend reinvestment & stock purchase plans	8,148	4	8,144
Employee stock purchase and incentive plans (in shares)		356,706
Employee stock purchase and incentive plans	(5,342)	4	(5,346)
Non-cash equity award compensation	13,547		13,547
Common dividends declared	(94,414)					(94,414)
Ending balance at Dec. 31, 2013	$ 1,245,783	$ 825	$ 1,760,899	$ 148,766	$ 806,298	$ (1,471,005)
Ending balance (in shares) at Dec. 31, 2013		82,504,801