Common Stock (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Common stock (Textual) [Abstract]
Common shares outstanding	4,977,633	5,663,556
Treasury stock outstanding, shares	22,400,000
Treasury stock outstanding, value	$ 4,526,000
Repurchased shares during the period, shares	1,017,588	644,562	0
Repurchased shares during the period, value	$ 689,300	$ 417,100	$ 0
Treasury stock reissued, shares	6,840,000
Reissued shares during the period, share	333,380	359,765	418,775