Available-for-Sale and Held-to-Maturity Securities (Narrative) (Details)	3 Months Ended
	Mar. 31, 2022 USD ($) Security	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Accrued interest receivable	$ 32,100		$ 27,400,000
Transfers from available for sale securities to held to maturity		$ 312,900,000
Gain On Transfer Of securities		0
Net realized gains (loss) resulting from sale of available-for-sale securities	0	$ 0
Financial instruments pledged as collateral	$ 569,700,000		639,600,000
Number of available for sale securities whose amortized costs exceeded their fair values | Security	201
Available-for-sale Securities, Continuous	$ 101,046,000
Available-for-sale Securities, Continuous Unrealized	15,957,000
Available-for-sale Securities, Continuous	$ 1,468,387,000
Percentage of available-for-sale portfolio	76.20%
Pledged [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Trading securities pledged	$ 1,200,000,000		1,200,000,000
Other Assets [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Accrued interest receivable	$ 28,300,000		$ 29,100,000