Consolidated Statement of Stockholders' Equity (USD $)
In Thousands, except Share data, unless otherwise specified
Total
Common Stock
Capital in Excess of Par Value
Accumulated Distributions in Excess of Earnings
Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2009 $ 1,521,984 $ 2,047 $ 1,762,904 $ (233,480) $ (9,487)
Beginning balance, shares at Dec. 31, 2009   204,662,620      
Increase (Decrease) in Stockholders' Equity [Roll Forward]          
Issuance of common stock, shares   7,037,054      
Issuance of common stock 61,377 70 61,307    
Distributions to investors (129,497)     (129,497)  
Other offering costs (9)   (9)    
Redemptions of common stock, share   (2,382,328)      
Redemptions of common stock (21,638) (24) (21,614)    
Stock compensation expense 7   7    
Changes in redeemable common stock 75,523   75,523    
Comprehensive income 52,628     30,430 22,198
Ending balance at Dec. 31, 2010 1,560,375 2,093 1,878,118 (332,547) 12,711
Ending balance, shares at Dec. 31, 2010   209,317,346      
Increase (Decrease) in Stockholders' Equity [Roll Forward]          
Issuance of common stock, shares   6,986,717      
Issuance of common stock 59,696 70 59,626    
Distributions to investors (131,063)     (131,063)  
Redemptions of common stock, share   (6,152,371)      
Redemptions of common stock (52,590) (62) (52,528)    
Changes in redeemable common stock (2,245)   (2,245)    
Comprehensive income 37,540     53,809 (16,269)
Ending balance at Dec. 31, 2011 1,471,713 2,101 1,882,971 (409,801) (3,558)
Ending balance, shares at Dec. 31, 2011 210,151,692 210,151,692      
Increase (Decrease) in Stockholders' Equity [Roll Forward]          
Issuance of common stock, shares   6,099,920      
Issuance of common stock 57,034 61 56,973    
Distributions to investors (131,308)     (131,308)  
Redemptions of common stock, share   (7,654,037)      
Redemptions of common stock (71,268) (76) (71,192)    
Changes in redeemable common stock 14,361   14,361    
Comprehensive income 26,774     25,397 1,377
Ending balance at Dec. 31, 2012 $ 1,367,306 $ 2,086 $ 1,883,113 $ (515,712) $ (2,181)
Ending balance, shares at Dec. 31, 2012 208,597,575 208,597,575