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Securities (Tables) | 3 Months Ended
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Mar. 31, 2020
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):
|  | March 31, 2020 |  | December 31, 2019
|  | Fair Value |  | Net Unrealized Gain (Loss) |  | Fair Value |  | Net Unrealized Gain (Loss)
U.S. government agency debentures |  | $ | 37,740 |  |  | $ | 264 |  |  | $ | 44,264 |  |  | $ | 6 |
Residential agency mortgage-backed securities |  | 1,922,725 |  |  | 26,195 |  |  | 1,504,651 |  |  | 2,293 |
Municipal and other tax-exempt securities |  | 35,513 |  |  | (289 | ) |  | 26,196 |  |  | 60 |
Asset-backed securities |  | 58,278 |  |  | (2,381 | ) |  | 14,084 |  |  | (21 | )
Other debt securities |  | 56,329 |  |  | (943 | ) |  | 34,726 |  |  | 21 |
Total trading securities |  | $ | 2,110,585 |  |  | $ | 22,846 |  |  | $ | 1,623,921 |  |  | $ | 2,359 |
Investment Securities (Held-to-Maturity) [Table Text Block] | The amortized cost and fair values of investment securities are as follows (in thousands):
|  | March 31, 2020
|  | Amortized |  | Fair |  | Gross Unrealized
|  | Cost |  | Value |  | Gain |  | Loss
Municipal and other tax-exempt |  | $ | 86,212 |  |  | $ | 89,359 |  |  | $ | 3,149 |  |  | $ | (2 | )
Residential agency mortgage-backed securities |  | 10,253 |  |  | 11,099 |  |  | 846 |  |  | — |
Other debt securities |  | 177,613 |  |  | 195,944 |  |  | 18,430 |  |  | (99 | )
Total investment securities |  | 274,078 |  |  | 296,402 |  |  | 22,425 |  |  | (101 | )
Allowance for credit losses1 |  | (1,502 | ) |  |  |  |  |  |
Investment securities, net of allowance |  | 272,576 |  |  | 296,402 |  |  | 22,425 |  |  | (101 | )
1 Effective with the adoption of FASB ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326) on January 1, 2020.
|  | December 31, 2019
|  | Amortized |  | Fair |  | Gross Unrealized
|  | Cost |  | Value |  | Gain |  | Loss
Municipal and other tax-exempt |  | $ | 93,653 |  |  | $ | 96,897 |  |  | $ | 3,250 |  |  | $ | (6 | )
Residential agency mortgage-backed securities |  | 10,676 |  |  | 11,164 |  |  | 488 |  |  | — |
Other debt securities |  | 189,089 |  |  | 206,341 |  |  | 17,547 |  |  | (295 | )
Total investment securities |  | $ | 293,418 |  |  | $ | 314,402 |  |  | $ | 21,285 |  |  | $ | (301 | )
The amortized cost and fair values of investment securities at March 31, 2020, 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 Maturity1
Fixed maturity debt securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  | $ | 38,058 |  |  | $ | 91,847 |  |  | $ | 122,431 |  |  | $ | 11,489 |  |  | $ | 263,825 |  |  | 5.12 |
Fair value |  | 38,380 |  |  | 97,946 |  |  | 137,365 |  |  | 11,612 |  |  | 285,303 |  |  |  |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  |  |  |  |  |  | $ | 10,253 |  |  | 2
Fair value |  |  |  |  |  |  |  |  |  |  |  |  |  | 11,099 |  |  |  |
Total investment securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  |  |  |  |  |  | $ | 274,078 |  |  |  |
Fair value |  |  |  |  |  |  |  |  |  |  |  |  |  | 296,402 |  |  |  |
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 4.7 years based upon current prepayment assumptions.
Temporarily Impaired Investment Securities (in thousands):
|  | March 31, 2020
|  | 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 |  | 2 |  |  | $ | 232 |  |  | $ | 1 |  |  | $ | 347 |  |  | $ | 1 |  |  | $ | 579 |  |  | $ | 2 |
Other debt securities |  | 8 |  |  | — |  |  | — |  |  | 5,168 |  |  | 99 |  |  | 5,168 |  |  | 99 |
Total investment securities |  | 10 |  |  | $ | 232 |  |  | $ | 1 |  |  | $ | 5,515 |  |  | $ | 100 |  |  | $ | 5,747 |  |  | $ | 101 |
|  | December 31, 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 |  | 4 |  |  | $ | 1,001 |  |  | $ | 1 |  |  | $ | 1,706 |  |  | $ | 5 |  |  | $ | 2,707 |  |  | $ | 6 |
Other debt securities |  | 13 |  |  | 275 |  |  | 1 |  |  | 8,041 |  |  | 294 |  |  | 8,316 |  |  | 295 |
Total investment securities |  | 17 |  |  | $ | 1,276 |  |  | $ | 2 |  |  | $ | 9,747 |  |  | $ | 299 |  |  | $ | 11,023 |  |  | $ | 301 |
Available For Sale Securities [Table Text Block] | The amortized cost and fair value of available for sale securities are as follows (in thousands):
|  | March 31, 2020
|  | Amortized |  | Fair |  | Gross Unrealized
|  | Cost |  | Value |  | Gain |  | Loss
U.S. Treasury |  | $ | 901 |  |  | $ | 917 |  |  | $ | 16 |  |  | $ | — |
Municipal and other tax-exempt |  | 23,166 |  |  | 24,034 |  |  | 872 |  |  | (4 | )
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |
Residential agency |  | 8,931,771 |  |  | 9,259,089 |  |  | 333,298 |  |  | (5,980 | )
Residential non-agency |  | 24,002 |  |  | 34,866 |  |  | 10,949 |  |  | (85 | )
Commercial agency |  | 3,277,948 |  |  | 3,374,899 |  |  | 103,953 |  |  | (7,002 | )
Other debt securities |  | 500 |  |  | 472 |  |  | — |  |  | (28 | )
Total available for sale securities |  | $ | 12,258,288 |  |  | $ | 12,694,277 |  |  | $ | 449,088 |  |  | $ | (13,099 | )
|  | December 31, 2019
|  | Amortized |  | Fair |  | Gross Unrealized
|  | Cost |  | Value |  | Gain |  | Loss
U.S. Treasury |  | $ | 1,598 |  |  | $ | 1,600 |  |  | $ | 2 |  |  | $ | — |
Municipal and other tax-exempt |  | 1,789 |  |  | 1,861 |  |  | 72 |  |  | — |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |
Residential agency |  | 7,956,297 |  |  | 8,046,096 |  |  | 104,912 |  |  | (15,113 | )
Residential non-agency |  | 25,968 |  |  | 41,609 |  |  | 15,641 |  |  | — |
Commercial agency |  | 3,145,342 |  |  | 3,178,005 |  |  | 37,808 |  |  | (5,145 | )
Other debt securities |  | 500 |  |  | 472 |  |  | — |  |  | (28 | )
Total available for sale securities |  | $ | 11,131,494 |  |  | $ | 11,269,643 |  |  | $ | 158,435 |  |  | $ | (20,286 | )
The amortized cost and fair values of available for sale securities at March 31, 2020, 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 Maturity1
Fixed maturity debt securities: |  |  |  |  |  |  |  |  |  |  |
Amortized cost | $ | 34,239 |  |  | $ | 1,223,377 |  |  | $ | 1,400,140 |  |  | $ | 644,759 |  |  | $ | 3,302,515 |  |  | 8.34 |
Fair value | 34,320 |  |  | 1,264,488 |  |  | 1,439,807 |  |  | 661,707 |  |  | 3,400,322 |  |  |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  | $ | 8,955,773 |  |  | 2
Fair value |  |  |  |  |  |  |  |  | 9,293,955 |  |  |
Total available-for-sale securities: |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  | $ | 12,258,288 |  |  |
Fair value |  |  |  |  |  |  |  |  | 12,694,277 |  |  |
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 3.3 years based upon current prepayment assumptions.
Sales of available for sale securities resulted in gains and losses as follows (in thousands):
| Three Months Ended March 31,
| 2020 |  | 2019
Proceeds | $ | 26,894 |  |  | $ | 245,259 |
Gross realized gains | 3 |  |  | 5,298 |
Gross realized losses | — |  |  | (5,222 | )
Related federal and state income tax expense (benefit) | 1 |  |  | 19 |
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value [Table Text Block] |
|  | March 31, 2020
|  | 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: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Municipal and other tax-exempt |  | 1 |  |  | $ | 1,621 |  |  | $ | 4 |  |  | $ | — |  |  | $ | — |  |  | $ | 1,621 |  |  | $ | 4 |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Residential agency |  | 37 |  |  | 314,479 |  |  | 2,230 |  |  | 177,225 |  |  | 3,750 |  |  | 491,704 |  |  | 5,980 |
Residential non-agency |  | 1 |  |  | 1,801 |  |  | 85 |  |  | — |  |  | — |  |  | 1,801 |  |  | 85 |
Commercial agency |  | 52 |  |  | 740,780 |  |  | 6,203 |  |  | 155,708 |  |  | 799 |  |  | 896,488 |  |  | 7,002 |
Other debt securities |  | 1 |  |  | — |  |  | — |  |  | 472 |  |  | 28 |  |  | 472 |  |  | 28 |
Total available for sale securities |  | 92 |  |  | $ | 1,058,681 |  |  | $ | 8,522 |  |  | $ | 333,405 |  |  | $ | 4,577 |  |  | $ | 1,392,086 |  |  | $ | 13,099 |
|  | December 31, 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: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Residential agency |  | 133 |  |  | $ | 1,352,597 |  |  | $ | 6,690 |  |  | $ | 686,002 |  |  | $ | 8,423 |  |  | $ | 2,038,599 |  |  | $ | 15,113 |
Commercial agency |  | 69 |  |  | 830,047 |  |  | 4,238 |  |  | 210,877 |  |  | 907 |  |  | 1,040,924 |  |  | 5,145 |
Other debt securities |  | 1 |  |  | — |  |  | — |  |  | 472 |  |  | 28 |  |  | 472 |  |  | 28 |
Total available for sale securities |  | 203 |  |  | $ | 2,182,644 |  |  | $ | 10,928 |  |  | $ | 897,351 |  |  | $ | 9,358 |  |  | $ | 3,079,995 |  |  | $ | 20,286 |
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):
|  | March 31, 2020 |  | December 31, 2019
|  | Fair Value |  | Net Unrealized Gain (Loss) |  | Fair Value |  | Net Unrealized Gain (Loss)
U.S. Treasury |  | $ | — |  |  | $ | — |  |  | $ | 9,917 |  |  | $ | (48 | )
Residential agency mortgage-backed securities |  | 1,703,238 |  |  | 60,083 |  |  | 1,088,660 |  |  | 14,109 |
Total |  | $ | 1,703,238 |  |  | $ | 60,083 |  |  | $ | 1,098,577 |  |  | $ | 14,061 |

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