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Securities (Tables) | 9 Months Ended
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Sep. 30, 2019
Marketable Securities [Abstract] |
Trading Securities, [Table Text Block] | The fair value and net unrealized gain (loss) included in trading securities are as follows (in thousands):
|  | September 30, 2019 |  | December 31, 2018
|  | Fair Value |  | Net Unrealized Gain (Loss) |  | Fair Value |  | Net Unrealized Gain (Loss)
U.S. government agency debentures |  | $ | 63,334 |  |  | $ | 23 |  |  | $ | 63,765 |  |  | $ | 254 |
Residential agency mortgage-backed securities |  | 1,480,458 |  |  | 3,851 |  |  | 1,791,584 |  |  | 9,966 |
Municipal and other tax-exempt securities |  | 44,105 |  |  | (99 | ) |  | 34,507 |  |  | (1 | )
Asset-backed securities |  | 36,928 |  |  | 50 |  |  | 42,656 |  |  | 685 |
Other debt securities |  | 50,387 |  |  | 116 |  |  | 24,411 |  |  | 65 |
Total trading securities |  | $ | 1,675,212 |  |  | $ | 3,941 |  |  | $ | 1,956,923 |  |  | $ | 10,969 |
Investment Securities (Held-to-Maturity) [Table Text Block] | The amortized cost and fair values of investment securities are as follows (in thousands):
|  | September 30, 2019
|  | Amortized |  | Fair |  | Gross Unrealized
|  | Cost |  | Value |  | Gain |  | Loss
Municipal and other tax-exempt |  | $ | 104,418 |  |  | $ | 107,647 |  |  | $ | 3,247 |  |  | $ | (18 | )
Residential agency mortgage-backed securities |  | 11,125 |  |  | 11,650 |  |  | 528 |  |  | (3 | )
Other debt securities |  | 188,681 |  |  | 204,724 |  |  | 16,457 |  |  | (414 | )
Total investment securities |  | $ | 304,224 |  |  | $ | 324,021 |  |  | $ | 20,232 |  |  | $ | (435 | )
|  | December 31, 2018
|  | Amortized |  | Fair |  | Gross Unrealized
|  | Cost |  | Value |  | Gain |  | Loss
Municipal and other tax-exempt |  | $ | 137,296 |  |  | $ | 138,562 |  |  | $ | 1,858 |  |  | $ | (592 | )
Residential agency mortgage-backed securities |  | 12,612 |  |  | 12,770 |  |  | 293 |  |  | (135 | )
Other debt securities |  | 205,279 |  |  | 215,966 |  |  | 12,257 |  |  | (1,570 | )
Total investment securities |  | $ | 355,187 |  |  | $ | 367,298 |  |  | $ | 14,408 |  |  | $ | (2,297 | )
The amortized cost and fair values of investment securities at September 30, 2019, by contractual maturity, are as shown in the following table (dollars in thousands):
|  | Less than One Year |  | One to Five Years |  | Six to Ten Years |  | Over Ten Years |  | Total |  | Weighted Average Maturity 1
Fixed maturity debt securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  | $ | 42,266 |  |  | $ | 93,139 |  |  | $ | 145,046 |  |  | $ | 12,648 |  |  | $ | 293,099 |  |  | 5.16 |
Fair value |  | 42,426 |  |  | 96,704 |  |  | 160,698 |  |  | 12,543 |  |  | 312,371 |  |  |  |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  |  |  |  |  |  | $ | 11,125 |  |  | 2
Fair value |  |  |  |  |  |  |  |  |  |  |  |  |  | 11,650 |  |  |  |
Total investment securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  |  |  |  |  |  | $ | 304,224 |  |  |  |
Fair value |  |  |  |  |  |  |  |  |  |  |  |  |  | 324,021 |  |  |  |
1 | Expected maturities may differ from contractual maturities, because borrowers may have the right to call or prepay obligations with or without penalty.
2 | The average expected lives of residential mortgage-backed securities were 4.5 years based upon current prepayment assumptions.
Temporarily Impaired Investment Securities (in thousands):
|  | September 30, 2019
|  | Number of Securities |  | Less Than 12 Months |  | 12 Months or Longer |  | Total
|  |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss
Investment: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal and other tax-exempt |  | 18 |  |  | $ | 10,302 |  |  | $ | 3 |  |  | $ | 2,213 |  |  | $ | 15 |  |  | $ | 12,515 |  |  | $ | 18 |
Residential agency mortgage-backed securities |  | 1 |  |  | 2,318 |  |  | 3 |  |  | — |  |  | — |  |  | 2,318 |  |  | 3 |
Other debt securities |  | 18 |  |  | 275 |  |  | 1 |  |  | 10,897 |  |  | 413 |  |  | 11,172 |  |  | 414 |
Total investment securities |  | 37 |  |  | $ | 12,895 |  |  | $ | 7 |  |  | $ | 13,110 |  |  | $ | 428 |  |  | $ | 26,005 |  |  | $ | 435 |
|  | December 31, 2018
|  | Number of Securities |  | Less Than 12 Months |  | 12 Months or Longer |  | Total
|  |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss
Investment: |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal and other tax-exempt |  | 72 |  |  | $ | 18,255 |  |  | $ | 69 |  |  | $ | 66,141 |  |  | $ | 523 |  |  | $ | 84,396 |  |  | $ | 592 |
Residential agency mortgage-backed securities |  | 2 |  |  | — |  |  | — |  |  | 5,633 |  |  | 135 |  |  | 5,633 |  |  | 135 |
Other debt securities |  | 72 |  |  | 13,372 |  |  | 64 |  |  | 23,028 |  |  | 1,506 |  |  | 36,400 |  |  | 1,570 |
Total investment securities |  | 146 |  |  | $ | 31,627 |  |  | $ | 133 |  |  | $ | 94,802 |  |  | $ | 2,164 |  |  | $ | 126,429 |  |  | $ | 2,297 |
Available For Sale Securities [Table Text Block] | The amortized cost and fair value of available for sale securities are as follows (in thousands):
|  | September 30, 2019
|  | Amortized |  | Fair |  | Gross Unrealized
|  | Cost |  | Value |  | Gain |  | Loss
U.S. Treasury |  | $ | 2,294 |  |  | $ | 2,296 |  |  | $ | 2 |  |  | $ | — |
Municipal and other tax-exempt |  | 1,772 |  |  | 1,848 |  |  | 76 |  |  | — |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |
Residential agency |  | 7,636,923 |  |  | 7,740,461 |  |  | 114,646 |  |  | (11,108 | )
Residential non-agency |  | 28,814 |  |  | 44,803 |  |  | 15,989 |  |  | — |
Commercial agency |  | 3,176,188 |  |  | 3,234,671 |  |  | 61,003 |  |  | (2,520 | )
Other debt securities |  | 500 |  |  | 472 |  |  | — |  |  | (28 | )
Total available for sale securities |  | $ | 10,846,491 |  |  | $ | 11,024,551 |  |  | $ | 191,716 |  |  | $ | (13,656 | )
|  | December 31, 2018
|  | Amortized |  | Fair |  | Gross Unrealized
|  | Cost |  | Value |  | Gain |  | Loss
U.S. Treasury |  | $ | 496 |  |  | $ | 493 |  |  | $ | — |  |  | $ | (3 | )
Municipal and other tax-exempt |  | 2,782 |  |  | 2,864 |  |  | 82 |  |  | — |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |
Residential agency |  | 5,886,323 |  |  | 5,804,708 |  |  | 16,149 |  |  | (97,764 | )
Residential non-agency |  | 40,948 |  |  | 59,736 |  |  | 18,788 |  |  | — |
Commercial agency |  | 2,986,297 |  |  | 2,953,889 |  |  | 7,955 |  |  | (40,363 | )
Other debt securities |  | 35,545 |  |  | 35,430 |  |  | 12 |  |  | (127 | )
Total available for sale securities |  | $ | 8,952,391 |  |  | $ | 8,857,120 |  |  | $ | 42,986 |  |  | $ | (138,257 | )
The amortized cost and fair values of available for sale securities at September 30, 2019, by contractual maturity, are as shown in the following table (dollars in thousands):
| Less than One Year |  | One to Five Years |  | Six to Ten Years |  | Over Ten Years |  | Total |  | Weighted Average Maturity 1
Fixed maturity debt securities: |  |  |  |  |  |  |  |  |  |  |
Amortized cost | $ | 35,845 |  |  | $ | 1,069,415 |  |  | $ | 1,476,121 |  |  | $ | 599,373 |  |  | $ | 3,180,754 |  |  | 8.29 |
Fair value | 35,806 |  |  | 1,081,571 |  |  | 1,512,308 |  |  | 609,602 |  |  | 3,239,287 |  |  |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  | $ | 7,665,737 |  |  | 2
Fair value |  |  |  |  |  |  |  |  | 7,785,264 |  |  |
Total available-for-sale securities: |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  | $ | 10,846,491 |  |  |
Fair value |  |  |  |  |  |  |  |  | 11,024,551 |  |  |
1 | Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without penalty.
2 | The average expected lives of residential mortgage-backed securities were 4.0 years based upon current prepayment assumptions.
Sales of available for sale securities resulted in gains and losses as follows (in thousands):
| Three Months Ended September 30, |  | Nine Months Ended September 30,
| 2019 |  | 2018 |  | 2019 |  | 2018
Proceeds | $ | 261,028 |  |  | $ | 45,293 |  |  | $ | 628,385 |  |  | $ | 232,826 |
Gross realized gains | 989 |  |  | 250 |  |  | 7,316 |  |  | 700 |
Gross realized losses | (984 | ) |  | — |  |  | (6,206 | ) |  | (1,502 | )
Related federal and state income tax expense (benefit) | 1 |  |  | 64 |  |  | 282 |  |  | (204 | )
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value [Table Text Block] | Temporarily Impaired Available for Sale Securities (in thousands)
|  | September 30, 2019
|  | Number of Securities |  | Less Than 12 Months |  | 12 Months or Longer |  | Total
|  |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss
Available for sale: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury |  | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Residential agency |  | 108 |  |  | 931,248 |  |  | 3,260 |  |  | 753,448 |  |  | 7,848 |  |  | 1,684,696 |  |  | 11,108 |
Commercial agency |  | 57 |  |  | 449,798 |  |  | 1,612 |  |  | 224,409 |  |  | 908 |  |  | 674,207 |  |  | 2,520 |
Other debt securities |  | 1 |  |  | — |  |  | — |  |  | 472 |  |  | 28 |  |  | 472 |  |  | 28 |
Total available for sale securities |  | 166 |  |  | $ | 1,381,046 |  |  | $ | 4,872 |  |  | $ | 978,329 |  |  | $ | 8,784 |  |  | $ | 2,359,375 |  |  | $ | 13,656 |
|  | December 31, 2018
|  | Number of Securities |  | Less Than 12 Months |  | 12 Months or Longer |  | Total
|  |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss |  | Fair Value |  | Unrealized Loss
Available for sale: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U.S. Treasury |  | 1 |  |  | $ | — |  |  | $ | — |  |  | $ | 493 |  |  | $ | 3 |  |  | $ | 493 |  |  | $ | 3 |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Residential agency |  | 289 |  |  | 510,824 |  |  | 1,158 |  |  | 3,641,370 |  |  | 96,606 |  |  | 4,152,194 |  |  | 97,764 |
Commercial agency |  | 197 |  |  | 179,258 |  |  | 394 |  |  | 1,969,504 |  |  | 39,969 |  |  | 2,148,762 |  |  | 40,363 |
Other debt securities |  | 3 |  |  | 9,982 |  |  | 63 |  |  | 20,436 |  |  | 64 |  |  | 30,418 |  |  | 127 |
Total available for sale securities |  | 490 |  |  | $ | 700,064 |  |  | $ | 1,615 |  |  | $ | 5,631,803 |  |  | $ | 136,642 |  |  | $ | 6,331,867 |  |  | $ | 138,257 |
Fair Value Option Securities [Table Text Block] | The fair value and net unrealized gain (loss) included in fair value option securities is as follows (in thousands):
|  | September 30, 2019 |  | December 31, 2018
|  | Fair Value |  | Net Unrealized Gain (Loss) |  | Fair Value |  | Net Unrealized Gain (Loss)
U.S. Treasury |  | $ | 552,536 |  |  | $ | 927 |  |  | $ | — |  |  | $ | — |
Residential agency mortgage-backed securities |  | 1,263,862 |  |  | 18,588 |  |  | 283,235 |  |  | 2,766 |
Total |  | $ | 1,816,398 |  |  | $ | 19,515 |  |  | $ | 283,235 |  |  | $ | 2,766 |

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