Repurchase Arrangements And Similar Borrowings, Including Related Hedging Activity (Narrative) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2012 Y	Dec. 31, 2011	Dec. 31, 2010 Y
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Swap agreements average expiration period (in months)	17
Notional amount of swap agreements			$ 100,000,000
Average fixed rates of interest rate swap agreements			4.09%
Term of LIBOR interest rate agreement (in years)	20		20
Derivatives held as cash flow hedges	26,900,000	30,200,000
Minimum [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Maturity period of repurchase arrangements (in days)	30
Maximum [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Maturity period of repurchase arrangements (in days)	90
Interest Rate Swap [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Swap agreements hedging short-term interest rates	700,000,000
Swap [Member]
Repurchase Arrangements And Similar Borrowings, Including Interest Rate Hedging Activity [Line Items]
Notional amount of swap agreements	$ 800,000,000