Available-For-Sale And Held-To-Maturity Securities (Narrative) (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2018 USD ($) security	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Proceeds from sale of available-for-sale securities		$ 372,400	$ 87,300	$ 0
Net realized gains (loss) resulting from sale of available-for-sale securities		(3,900)	400
Unrealized gains (losses) recorded in accumulated other comprehensive loss	[1],[2],[3]	(36,254)	4,730	5,803
Financial instruments pledged as collateral		$ 1,900,000	2,200,000
Number of available for sale securities whose amortized costs exceeded their fair values | security		258
Available-for-sale Securities, Continuous		$ 55,904
Available-for-sale Securities, Continuous Unrealized		33,930
Available-for-sale Securities, Continuous		$ 2,626,686
Percentage of available-for-sale portfolio		85.50%
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security		196
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss		$ 102,024
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss		30,205
Credit-related OTTI		0	0	$ 0
Gross unrealized losses related to investment portfolio		157,900
Pledged [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Trading securities pledged		$ 1,600,000	$ 2,000,000

[1] Amounts are net of reclassifications to earnings of realized losses of $2.9 and realized gains of $0.2 million for the years ended December 31, 2018 and 2017, respectively. There were no reclassifications to earnings of realized gains for the year ended December 31, 2016.

[2] Net of a tax benefit of $11.2 million and tax expenses of $3.3 million and $0.3 million for the years ended December 31, 2018, 2017, and 2016, 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. The reclassification is reflected in the activity for the year ended December 31, 2018. See Note 2 for further details.