Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity (Details)

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Shareholders' Equity (Details) (USD $)
Share data in Thousands, except Per Share data, unless otherwise specified
12 Months Ended 1 Months Ended 12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Jun. 30, 2012
At The Market Offering Program [Member]
Dec. 31, 2013
Common Stock [Member]
Dec. 31, 2012
Common Stock [Member]
Dec. 31, 2011
Common Stock [Member]
Dec. 31, 2013
Additional Paid In Capital [Member]
Dec. 31, 2012
Additional Paid In Capital [Member]
Dec. 31, 2011
Additional Paid In Capital [Member]
Financing Agreements [Line Items]                    
Issuance and sale of stock, term       36 months            
Common stock reserved for future issuance $ 250,000,000                  
Common shares issued 66,531 66,437                
Shares issued under Dividend Reinvestment Program, shares         0 55 170      
Weighted average issue price, dividend reinvestment program $ 0.00 $ 29.67 $ 29.97              
Net proceeds, dividend reinvestment program 0 1,316,000 5,043,000              
Stock Issued During Period, Value, Dividend Reinvestment Plan   $ 1,316,000 $ 5,043,000     $ 1,000 $ 2,000 $ 0 $ 1,315,000 $ 5,041,000