Short-Term Borrowings and Long-Term Debt Repurchase Agreements (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Short-term Debt [Line Items]
Short-term Debt	$ 597,033	$ 674,077	$ 868,940
Repurchase Agreements [Member]
Short-term Debt [Line Items]
Short-term Debt	186,735	204,800	259,458
Short-term Debt, Weighted Average Interest Rate	0.12%	0.28%	0.42%
Short-term Debt, Average Outstanding Amount	$ 208,144	$ 252,633	$ 254,662
Debt Instrument, Interest Rate During Period	0.13%	0.31%	0.55%