Annual report pursuant to Section 13 and 15(d)

Shareholders' Equity (Details)

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Shareholders' Equity (Details) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Equity [Abstract]      
Stock repurchase plan, authorized amount $ 500,000,000    
Aggregate shares repurchased under stock repurchase plan 9,593,278    
Stock repurchased to date, value 441,443,000    
Stock repurchased during period, value $ 206,000 $ 20,000,000 $ 13,838,000