Available-For-Sale And Held-To-Maturity Securities (Narrative) (Details) $ in Thousands		3 Months Ended
		Mar. 31, 2017 USD ($) security	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Proceeds from sale of available-for-sale securities		$ 0	$ 0
Unrealized gains (losses) recorded in accumulated other comprehensive loss	[1]	3,777	(1,028)
Financial instruments pledged as collateral		1,900,000		$ 2,000,000
Trading securities pledged		$ 1,900,000		1,700,000
Number of available for sale securities whose amortized costs exceeded their fair values | security		130
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		$ 17,357
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses		4,545
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		$ 1,090,977
Percentage of available-for-sale portfolio		32.30%
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security		43
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss		$ 19,280
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss		2,189
Credit-related OTTI		0	$ 0
Gross unrealized losses related to investment portfolio	[2]	17,357		$ 20,411
Available-for-sale and Held-to-maturity Securities [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Gross unrealized losses related to investment portfolio		$ 36,600

[1] There were no reclassifications to earnings during the three months ended March 31, 2017 and 2016, respectively.

[2] Unrealized gains/(losses) related to available-for-sale securities are reported in accumulated other comprehensive loss.