Investments (Narrative) (Details) (USD $)	9 Months Ended
	Sep. 30, 2011 investments reportablesegment interestrateswaps	Dec. 31, 2010	Sep. 30, 2010
Schedule of Investments [Line Items]
Investment securities, aggregate fair value, continuous unrealized losses of more than 12 months	$ 2,122,000
Investment securities, aggregate unrealized loss, continuous unrealized losses of more than 12 months	76,000
Number of investments in continuous unrealized loss position for more than twelve months	19
Unrealized Losses Related To Marketability Of Securities Or Issuers Ability To Honor Redemption Obligations	0
Investment value deemed to be OTTI	0
Investment securities, aggregate carrying value, pledged as collateral	$ 2,563,412,000	$ 2,096,850,000	$ 2,015,500,000