Available-For-Sale And Held-To-Maturity Securities (Narrative) (Details)		3 Months Ended		6 Months Ended
		Jun. 30, 2019 USD ($) security	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) security	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Proceeds from sale of available-for-sale securities		$ 155,300,000		$ 155,300,000	$ 0
Net realized gains (loss) resulting from sale of available-for-sale securities		(300,000)		(300,000)
Unrealized gains (losses) recorded in accumulated other comprehensive loss	[1],[2],[3]	16,284,000	$ (11,856,000)	42,084,000	(24,927,000)
Financial instruments pledged as collateral		$ 1,300,000,000		$ 1,300,000,000		$ 1,900,000,000
Number of available for sale securities whose amortized costs exceeded their fair values | security		143		143
Available-for-sale Securities, Continuous		$ 11,077,000		$ 11,077,000
Available-for-sale Securities, Continuous Unrealized		6,240,000		6,240,000
Available-for-sale Securities, Continuous		$ 1,351,479,000		$ 1,351,479,000
Percentage of available-for-sale portfolio		50.00%		50.00%
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security		136		136
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss		$ 35,626,000		$ 35,626,000
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss		26,547,000		26,547,000
Credit-related OTTI		0	$ 0	0	$ 0
Gross unrealized losses related to investment portfolio				46,700,000
Pledged [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Trading securities pledged		$ 1,300,000,000		$ 1,300,000,000		$ 1,600,000,000

[1] Net of reclassifications to earnings of realized losses of $0.2 million for the three and six months ended June 30, 2019. There were no reclassifications to earnings during the six months ended June 30, 2018.

[2] Net of tax expense of $3.9 million and tax benefit of $6.0 million for the three months ended June 30, 2019 and 2018, respectively. Net of tax expense of $13.7 million and tax benefit of $8.3 million for the six months ended June 30, 2019 and 2018, respectively.

[3] The adoption of ASU 2018-02 on January 1, 2018 resulted in a reclassification of $3.1 million to retained earnings related to cash flow hedges and investment portfolio risk