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Available-For-Sale And Held-To-Maturity Securities (Narrative) (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 USD ($) security | Dec. 31, 2016 USD ($) | Dec. 31, 2015 USD ($)
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items] |  |  |  |
Proceeds from sale of available-for-sale securities |  | $ 87,300 | $ 0 | $ 641,600
Net realized gains resulting from sale of available-for-sale securities |  | 400 |  | 3,200
Unrealized gains (losses) recorded in accumulated other comprehensive loss | [1],[2] | 4,730 | 5,803 | 1,389
Financial instruments pledged as collateral |  | 2,200,000 | 2,000,000 |
Trading securities pledged |  | $ 2,000,000 | 1,700,000 |
Number of available for sale securities whose amortized costs exceeded their fair values | security |  | 186 |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses |  | $ 20,789 |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Losses |  | 12,257 |  |
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value |  | $ 1,284,490 |  |
Percentage of available-for-sale portfolio |  | 34.00% |  |
Held-to-maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions | security |  | 42 |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss |  | $ 18,107 |  |
Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Aggregate Loss |  | 17,298 |  |
Credit-related OTTI |  | 0 | 0 | $ 0
Gross unrealized losses related to investment portfolio | [3] | 20,789 | $ 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 |  | $ 38,900 |  |
[1] | Net of taxes of $3.3 million, $0.3 million, and $0.7 million for the years ended December 31, 2017, 2016, and 2015, respectively.
[2] | There were no reclassifications to earnings of realized gains for the years ended December 31, 2017 and 2016. Amounts are net of reclassifications to earnings of realized gains of $2.1 million for the year ended December 31, 2015.
[3] | Unrealized gains/(losses) related to available-for-sale securities are reported in accumulated other comprehensive loss.

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- Definition Amount of unrealized loss on securities classified as available-for-sale that have been in a loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
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- Definition Amount of unrealized loss on securities classified as available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
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