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Available-For-Sale And Held-To-Maturity Securities (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Aug. 01, 2019 USD ($)
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Proceeds from sale of available-for-sale securities	$ 641,800	$ 372,400	$ 87,300
Net realized gains (loss) resulting from sale of available-for-sale securities	(300)	(3,900)	400
Transfers from held to maturity to available for sale securities reclassification fair value				$ 1,100,000
Other comprehensive income (loss), transfers from held-to-maturity to available-for-sale securities, net of tax	17,900
Unrealized gains (losses) recorded in accumulated other comprehensive loss	42,400	(36,300)	4,700
Financial instruments pledged as collateral	$ 801,500	1,900,000
Number of available for sale securities whose amortized costs exceeded their fair values | security	125
Available-for-sale Securities, Continuous	$ 14,793
Available-for-sale Securities, Continuous Unrealized	6,472
Available-for-sale Securities, Continuous	$ 1,624,169
Percentage of available-for-sale portfolio	49.90%
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security	125
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss	$ 34,300
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss	31,400
Credit-related OTTI	0	0	$ 0
Gross unrealized losses related to investment portfolio	49,100
Pledged [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Trading securities pledged	$ 816,100	$ 1,600,000

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