Available-For-Sale And Held-To-Maturity Securities (Narrative) (Details) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018 USD ($) security	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) security	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Proceeds from sale of available-for-sale securities		$ 55,400	$ 0	$ 55,400	$ 87,300
Net realized gains (loss) resulting from sale of available-for-sale securities		(400)		(400)	400
Unrealized gains (losses) recorded in accumulated other comprehensive loss	[1],[2],[3]	(3,138)	4,736	(28,065)	12,283
Financial instruments pledged as collateral		$ 2,000,000		$ 2,000,000		$ 2,200,000
Number of available for sale securities whose amortized costs exceeded their fair values | security		232		232
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		$ 49,209		$ 49,209
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		26,542		26,542
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		$ 1,764,637		$ 1,764,637
Percentage of available-for-sale portfolio		52.70%		52.70%
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security		152		152
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss		$ 64,008		$ 64,008
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss		39,563		39,563
Credit-related OTTI		0	$ 0	0	$ 0
Gross unrealized losses related to investment portfolio				113,200
Pledged [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Trading securities pledged		$ 2,100,000		$ 2,100,000		$ 2,000,000

[1] Net of tax benefit of $2.1 million and tax expense of $5.0 million for the three months ended September 30, 2018 and 2017, respectively. Net of tax benefit of $10.4 million and tax expense of $13.5 million for the nine months ended September 30, 2018 and 2017, respectively.

[2] The adoption of ASU 2018-02 on January 1, 2018 resulted in a reclassification of $3.0 million to retained earnings related to cash flow hedges and investment portfolio risk. The reclassification is reflected in the activity for the nine months ended September 30, 2018. See Note 2 for further details.

[3] There were no reclassifications to earnings during the three and nine months ended September 30, 2018 and 2017, respectively.