XML 33 R23.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Securities (Tables) | 6 Months Ended
--- | ---
Jun. 30, 2018
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):
|  | June 30, 2018 |  | December 31, 2017 |  | June 30, 2017
|  | Fair Value |  | Net Unrealized Gain (Loss) |  | Fair Value |  | Net Unrealized Gain (Loss) |  | Fair Value |  | Net Unrealized Gain (Loss)
U.S. government agency debentures |  | $ | 28,750 |  |  | $ | 10 |  |  | $ | 21,196 |  |  | $ | 8 |  |  | $ | 20,954 |  |  | $ | (9 | )
U.S. government agency residential mortgage-backed securities |  | 1,605,001 |  |  | 1,923 |  |  | 392,673 |  |  | (517 | ) |  | 365,171 |  |  | (1,032 | )
Municipal and other tax-exempt securities |  | 70,606 |  |  | 231 |  |  | 13,559 |  |  | 83 |  |  | 45,444 |  |  | 230 |
Asset-backed securities |  | 193,271 |  |  | 250 |  |  | 23,885 |  |  | (26 | ) |  | — |  |  | — |
Other trading securities |  | 11,987 |  |  | 32 |  |  | 11,363 |  |  | 4 |  |  | 9,845 |  |  | (175 | )
Total trading securities |  | $ | 1,909,615 |  |  | $ | 2,446 |  |  | $ | 462,676 |  |  | $ | (448 | ) |  | $ | 441,414 |  |  | $ | (986 | )
Investment Securities (Held-to-Maturity) [Table Text Block] | The amortized cost and fair values of investment securities are as follows (in thousands):
|  | June 30, 2018
|  | Amortized |  | Fair |  | Gross Unrealized
|  | Cost |  | Value |  | Gain |  | Loss
Municipal and other tax-exempt |  | $ | 173,097 |  |  | $ | 174,205 |  |  | $ | 1,779 |  |  | $ | (671 | )
U.S. government agency residential mortgage-backed securities |  | 13,989 |  |  | 13,984 |  |  | 232 |  |  | (237 | )
Other debt securities |  | 204,927 |  |  | 215,195 |  |  | 12,259 |  |  | (1,991 | )
Total investment securities |  | $ | 392,013 |  |  | $ | 403,384 |  |  | $ | 14,270 |  |  | $ | (2,899 | )
|  | December 31, 2017
|  | Amortized |  | Fair |  | Gross Unrealized
|  | Cost |  | Value |  | Gain |  | Loss
Municipal and other tax-exempt |  | $ | 228,186 |  |  | $ | 230,349 |  |  | $ | 2,967 |  |  | $ | (804 | )
U.S. government agency residential mortgage-backed securities |  | 15,891 |  |  | 16,242 |  |  | 446 |  |  | (95 | )
Other debt securities |  | 217,716 |  |  | 233,444 |  |  | 17,095 |  |  | (1,367 | )
Total investment securities |  | $ | 461,793 |  |  | $ | 480,035 |  |  | $ | 20,508 |  |  | $ | (2,266 | )
|  | June 30, 2017
|  | Amortized |  | Fair |  | Gross Unrealized
|  | Cost |  | Value |  | Gain |  | Loss
Municipal and other tax-exempt |  | $ | 267,375 |  |  | $ | 270,531 |  |  | $ | 3,384 |  |  | $ | (228 | )
U.S. government agency residential mortgage-backed securities |  | 18,035 |  |  | 18,642 |  |  | 668 |  |  | (61 | )
Other debt securities |  | 205,016 |  |  | 226,502 |  |  | 22,040 |  |  | (554 | )
Total investment securities |  | $ | 490,426 |  |  | $ | 515,675 |  |  | $ | 26,092 |  |  | $ | (843 | )
The amortized cost and fair values of investment securities at June 30, 2018, 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 Maturity²
Municipal and other tax-exempt: |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  | $ | 60,535 |  |  | $ | 62,005 |  |  | $ | 28,117 |  |  | $ | 22,440 |  |  | $ | 173,097 |  |  | 4.02 |
Fair value |  | 60,487 |  |  | 61,736 |  |  | 29,038 |  |  | 22,944 |  |  | 174,205 |  |  |
Nominal yield¹ |  | 2.07 | % |  | 2.58 | % |  | 5.81 | % |  | 5.12 | % |  | 3.25 | % |  |
Other debt securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  | 14,877 |  |  | 52,170 |  |  | 123,762 |  |  | 14,118 |  |  | 204,927 |  |  | 5.99 |
Fair value |  | 15,023 |  |  | 54,233 |  |  | 132,912 |  |  | 13,027 |  |  | 215,195 |  |  |
Nominal yield |  | 3.99 | % |  | 4.69 | % |  | 5.67 | % |  | 4.34 | % |  | 5.21 | % |  |
Total fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  | $ | 75,412 |  |  | $ | 114,175 |  |  | $ | 151,879 |  |  | $ | 36,558 |  |  | $ | 378,024 |  |  | 5.08 |
Fair value |  | 75,510 |  |  | 115,969 |  |  | 161,950 |  |  | 35,971 |  |  | 389,400 |  |  |  |
Nominal yield |  | 2.45 | % |  | 3.54 | % |  | 5.69 | % |  | 4.82 | % |  | 4.31 | % |  |  |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  |  |  |  |  |  | $ | 13,989 |  |  | ³ |
Fair value |  |  |  |  |  |  |  |  |  |  |  |  |  | 13,984 |  |  |  |
Nominal yield4 |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.76 | % |  |  |
Total investment securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  |  |  |  |  |  | $ | 392,013 |  |  |  |
Fair value |  |  |  |  |  |  |  |  |  |  |  |  |  | 403,384 |  |  |  |
Nominal yield |  |  |  |  |  |  |  |  |  |  |  |  |  | 4.26 | % |  |  |
1 | Calculated on a taxable equivalent basis using a 25 percent effective tax rate.
2 | Expected maturities may differ from contractual maturities, because borrowers may have the right to call or prepay obligations with or without penalty.
3 | The average expected lives of residential mortgage-backed securities were 5.0 years based upon current prepayment assumptions.
4 | The nominal yield on residential mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary - Unaudited for current yields on the investment securities portfolio.
Available For Sale Securities [Table Text Block] | The amortized cost and fair value of available for sale securities are as follows (in thousands):
|  | June 30, 2018
|  | Amortized |  | Fair |  | Gross Unrealized |  |
|  | Cost |  | Value |  | Gain |  | Loss |  | OTTI
U.S. Treasury |  | $ | 494 |  |  | $ | 490 |  |  | $ | — |  |  | $ | (4 | ) |  | $ | — |
Municipal and other tax-exempt |  | 10,590 |  |  | 10,697 |  |  | 111 |  |  | (4 | ) |  | — |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U. S. government agencies: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FNMA |  | 3,088,585 |  |  | 3,007,885 |  |  | 2,774 |  |  | (83,474 | ) |  | — |
FHLMC |  | 1,580,185 |  |  | 1,538,582 |  |  | 738 |  |  | (42,341 | ) |  | — |
GNMA |  | 772,785 |  |  | 758,093 |  |  | 915 |  |  | (15,607 | ) |  | — |
Total U.S. government agencies |  | 5,441,555 |  |  | 5,304,560 |  |  | 4,427 |  |  | (141,422 | ) |  | — |
Private issue |  | 65,376 |  |  | 83,224 |  |  | 18,221 |  |  | — |  |  | (373 | )
Total residential mortgage-backed securities |  | 5,506,931 |  |  | 5,387,784 |  |  | 22,648 |  |  | (141,422 | ) |  | (373 | )
Commercial mortgage-backed securities guaranteed by U.S. government agencies |  | 2,799,953 |  |  | 2,738,451 |  |  | 1,815 |  |  | (63,317 | ) |  | — |
Other debt securities |  | 25,500 |  |  | 25,444 |  |  | 12 |  |  | (68 | ) |  | — |
Total available for sale securities |  | $ | 8,343,468 |  |  | $ | 8,162,866 |  |  | $ | 24,586 |  |  | $ | (204,815 | ) |  | $ | (373 | )
|  | December 31, 2017
|  | Amortized |  | Fair |  | Gross Unrealized |  |
|  | Cost |  | Value |  | Gain |  | Loss |  | OTTI
U.S. Treasury |  | $ | 1,000 |  |  | $ | 1,000 |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Municipal and other tax-exempt |  | 27,182 |  |  | 27,080 |  |  | 181 |  |  | (283 | ) |  | — |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |
U. S. government agencies: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FNMA |  | 3,021,551 |  |  | 2,997,563 |  |  | 11,549 |  |  | (35,537 | ) |  | — |
FHLMC |  | 1,545,971 |  |  | 1,531,009 |  |  | 3,148 |  |  | (18,110 | ) |  | — |
GNMA |  | 787,626 |  |  | 780,580 |  |  | 1,607 |  |  | (8,653 | ) |  | — |
Total U.S. government agencies |  | 5,355,148 |  |  | 5,309,152 |  |  | 16,304 |  |  | (62,300 | ) |  | — |
Private issue |  | 74,311 |  |  | 93,221 |  |  | 19,301 |  |  | — |  |  | (391 | )
Total residential mortgage-backed securities |  | 5,429,459 |  |  | 5,402,373 |  |  | 35,605 |  |  | (62,300 | ) |  | (391 | )
Commercial mortgage-backed securities guaranteed by U.S. government agencies |  | 2,858,885 |  |  | 2,834,961 |  |  | 1,963 |  |  | (25,887 | ) |  | — |
Other debt securities |  | 25,500 |  |  | 25,481 |  |  | 50 |  |  | (69 | ) |  | — |
Perpetual preferred stock |  | 12,562 |  |  | 15,767 |  |  | 3,205 |  |  | — |  |  | — |
Equity securities and mutual funds |  | 14,487 |  |  | 14,916 |  |  | 515 |  |  | (86 | ) |  | — |
Total available for sale securities |  | $ | 8,369,075 |  |  | $ | 8,321,578 |  |  | $ | 41,519 |  |  | $ | (88,625 | ) |  | $ | (391 | )
|  | June 30, 2017
|  | Amortized |  | Fair |  | Gross Unrealized |  |
|  | Cost |  | Value |  | Gain |  | Loss |  | OTTI
U.S. Treasury |  | $ | 1,000 |  |  | $ | 998 |  |  | $ | — |  |  | $ | (2 | ) |  | $ | — |
Municipal and other tax-exempt |  | 32,885 |  |  | 32,765 |  |  | 293 |  |  | (413 | ) |  | — |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |
U. S. government agencies: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FNMA |  | 3,005,920 |  |  | 3,008,531 |  |  | 24,213 |  |  | (21,602 | ) |  | — |
FHLMC |  | 1,412,376 |  |  | 1,412,472 |  |  | 7,785 |  |  | (7,689 | ) |  | — |
GNMA |  | 938,086 |  |  | 936,365 |  |  | 3,641 |  |  | (5,362 | ) |  | — |
Other |  | 25,000 |  |  | 25,009 |  |  | 52 |  |  | (43 | ) |  | — |
Total U.S. government agencies |  | 5,381,382 |  |  | 5,382,377 |  |  | 35,691 |  |  | (34,696 | ) |  | — |
Private issue |  | 86,656 |  |  | 103,383 |  |  | 16,727 |  |  | — |  |  | — |
Total residential mortgage-backed securities |  | 5,468,038 |  |  | 5,485,760 |  |  | 52,418 |  |  | (34,696 | ) |  | — |
Commercial mortgage-backed securities guaranteed by U.S. government agencies |  | 2,788,543 |  |  | 2,782,070 |  |  | 7,804 |  |  | (14,277 | ) |  | — |
Other debt securities |  | 4,400 |  |  | 4,152 |  |  | — |  |  | (248 | ) |  | — |
Perpetual preferred stock |  | 12,562 |  |  | 16,568 |  |  | 4,006 |  |  | — |  |  | — |
Equity securities and mutual funds |  | 17,572 |  |  | 18,728 |  |  | 1,219 |  |  | (63 | ) |  | — |
Total available for sale securities |  | $ | 8,325,000 |  |  | $ | 8,341,041 |  |  | $ | 65,740 |  |  | $ | (49,699 | ) |  | $ | — |
The amortized cost and fair values of available for sale securities at June 30, 2018, 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 Maturity4
U.S. Treasuries: |  |  |  |  |  |  |  |  |  |  |
Amortized cost | $ | — |  |  | $ | 494 |  |  | $ | — |  |  | $ | — |  |  | $ | 494 |  |  | 1.59 |
Fair value | — |  |  | 490 |  |  | — |  |  | — |  |  | 490 |  |  |
Nominal yield | — | % |  | 1.99 | % |  | — | % |  | — | % |  | 1.99 | % |  |
Municipal and other tax-exempt: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost | $ | 4,574 |  |  | $ | 2,303 |  |  | $ | — |  |  | $ | 3,713 |  |  | $ | 10,590 |  |  | 6.53 |
Fair value | 4,580 |  |  | 2,401 |  |  | — |  |  | 3,716 |  |  | 10,697 |  |  |
Nominal yield¹ | 3.45 | % |  | 6.27 | % |  | — | % |  | 3.98 | % | 5 | 4.25 | % |  |
Commercial mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |
Amortized cost | $ | 8,070 |  |  | $ | 987,244 |  |  | $ | 1,548,520 |  |  | $ | 256,119 |  |  | $ | 2,799,953 |  |  | 6.89 |
Fair value | 8,041 |  |  | 968,540 |  |  | 1,512,106 |  |  | 249,764 |  |  | 2,738,451 |  |  |
Nominal yield | 1.67 | % |  | 1.96 | % |  | 2.17 | % |  | 2.20 | % |  | 2.10 | % |  |
Other debt securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | 25,500 |  |  | $ | 25,500 |  |  | 14.18 |
Fair value | — |  |  | — |  |  | — |  |  | 25,444 |  |  | 25,444 |  |  |
Nominal yield | — | % |  | — | % |  | — | % |  | 1.59 | % | 5 | 1.59 | % |  |
Total fixed maturity securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost | $ | 12,644 |  |  | $ | 990,041 |  |  | $ | 1,548,520 |  |  | $ | 285,332 |  |  | $ | 2,836,537 |  |  | 6.95 |
Fair value | 12,621 |  |  | 971,431 |  |  | 1,512,106 |  |  | 278,924 |  |  | 2,775,082 |  |  |
Nominal yield | 2.31 | % |  | 1.97 | % |  | 2.17 | % |  | 2.17 | % |  | 2.10 | % |  |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  |  |  |  |  | $ | 5,506,931 |  |  | 2 |
Fair value |  |  |  |  |  |  |  |  |  |  |  |  | 5,387,784 |  |  |
Nominal yield3 |  |  |  |  |  |  |  |  |  |  |  |  | 2.16 | % |  |
Total available-for-sale securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortized cost |  |  |  |  |  |  |  |  |  |  |  |  | $ | 8,343,468 |  |  |  |
Fair value |  |  |  |  |  |  |  |  |  |  |  |  | 8,162,866 |  |  |  |
Nominal yield |  |  |  |  |  |  |  |  |  |  |  |  | 2.14 | % |  |  |
1 | Calculated on a taxable equivalent basis using a 25 percent effective tax rate.
2 | The average expected lives of mortgage-backed securities were 4.3 years years based upon current prepayment assumptions.
3 | The nominal yield on mortgage-backed securities is based upon prepayment assumptions at the purchase date. Actual yields earned may differ significantly based upon actual prepayments. See Quarterly Financial Summary –– Unaudited following for current yields on available for sale securities portfolio.
4 | Expected maturities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without penalty.
5 | Nominal yield on municipal and other tax-exempt securities and other debt securities with contractual maturity dates over ten years are based on variable rates which generally are reset within 35.
Sales of available for sale securities resulted in gains and losses as follows (in thousands):
| Three Months Ended June 30, |  | Six Months Ended June 30,
| 2018 |  | 2017 |  | 2018 |  | 2017
Proceeds | $ | 142,743 |  |  | $ | 460,402 |  |  | $ | 187,533 |  |  | $ | 700,412 |
Gross realized gains | 257 |  |  | 2,763 |  |  | 450 |  |  | 4,855 |
Gross realized losses | (1,019 | ) |  | (2,383 | ) |  | (1,502 | ) |  | (2,426 | )
Related federal and state income tax expense (benefit) | (194 | ) |  | 148 |  |  | (268 | ) |  | 945 |
Securities Pledged As Collateral [Table Text Block] | A summary of investment and available for sale securities that have been pledged as collateral for repurchase agreements, public trust funds on deposit and for other purposes, as required by law was as follows (in thousands):
| June 30, 2018 |  | Dec. 31, 2017 |  | June 30, 2017
Investment: |  |  |  |  |
Amortized cost | $ | 172,906 |  |  | $ | 226,852 |  |  | $ | 251,684 |
Fair value | 174,240 |  |  | 229,429 |  |  | 255,097 |
Available for sale: |  |  |  |  |
Amortized cost | 6,821,287 |  |  | 7,151,468 |  |  | 6,327,666 |
Fair value | 6,653,875 |  |  | 7,089,346 |  |  | 6,317,623 |
Schedule of Unrealized Loss on Investments [Table Text Block] | Temporarily Impaired Securities as of June 30, 2018 (in thousands):
|  | 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 |  | 84 |  |  | $ | 98,325 |  |  | $ | 484 |  |  | $ | 5,007 |  |  | $ | 187 |  |  | $ | 103,332 |  |  | $ | 671 |
U.S. government agency residential mortgage-backed securities |  | 3 |  |  | 6,979 |  |  | 110 |  |  | 2,809 |  |  | 127 |  |  | 9,788 |  |  | 237 |
Other debt securities |  | 80 |  |  | 36,131 |  |  | 1,795 |  |  | 3,324 |  |  | 196 |  |  | 39,455 |  |  | 1,991 |
Total investment securities |  | 167 |  |  | $ | 141,435 |  |  | $ | 2,389 |  |  | $ | 11,140 |  |  | $ | 510 |  |  | $ | 152,575 |  |  | $ | 2,899 |
|  | 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 |  |  | $ | 490 |  |  | $ | 4 |  |  | $ | — |  |  | $ | — |  |  | $ | 490 |  |  | $ | 4 |
Municipal and other tax-exempt |  | 10 |  |  | 4,784 |  |  | 3 |  |  | 495 |  |  | 1 |  |  | 5,279 |  |  | 4 |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U. S. government agencies: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FNMA |  | 174 |  |  | 2,049,432 |  |  | 44,860 |  |  | 710,962 |  |  | 38,614 |  |  | 2,760,394 |  |  | 83,474 |
FHLMC |  | 93 |  |  | 1,116,337 |  |  | 26,663 |  |  | 339,515 |  |  | 15,678 |  |  | 1,455,852 |  |  | 42,341 |
GNMA |  | 33 |  |  | 275,104 |  |  | 5,611 |  |  | 220,740 |  |  | 9,996 |  |  | 495,844 |  |  | 15,607 |
Total U.S. government agencies |  | 300 |  |  | 3,440,873 |  |  | 77,134 |  |  | 1,271,217 |  |  | 64,288 |  |  | 4,712,090 |  |  | 141,422 |
Private issue1 |  | 8 |  |  | 5,409 |  |  | 373 |  |  | — |  |  | — |  |  | 5,409 |  |  | 373 |
Total residential mortgage-backed securities |  | 308 |  |  | 3,446,282 |  |  | 77,507 |  |  | 1,271,217 |  |  | 64,288 |  |  | 4,717,499 |  |  | 141,795 |
Commercial mortgage-backed securities guaranteed by U.S. government agencies |  | 211 |  |  | 1,675,839 |  |  | 42,732 |  |  | 554,819 |  |  | 20,585 |  |  | 2,230,658 |  |  | 63,317 |
Other debt securities |  | 2 |  |  | — |  |  | — |  |  | 20,434 |  |  | 68 |  |  | 20,434 |  |  | 68 |
Total available for sale securities |  | 532 |  |  | $ | 5,127,395 |  |  | $ | 120,246 |  |  | $ | 1,846,965 |  |  | $ | 84,942 |  |  | $ | 6,974,360 |  |  | $ | 205,188 |
1 | Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income.
Temporarily Impaired Securities as of December 31, 2017 (In thousands)
|  | 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 |  | 100 |  |  | $ | 145,960 |  |  | $ | 643 |  |  | $ | 5,833 |  |  | $ | 161 |  |  | $ | 151,793 |  |  | $ | 804 |
U.S. government agency residential mortgage-backed securities |  | 1 |  |  | — |  |  | — |  |  | 3,356 |  |  | 95 |  |  | 3,356 |  |  | 95 |
Other debt securities |  | 49 |  |  | 20,091 |  |  | 1,238 |  |  | 3,076 |  |  | 129 |  |  | 23,167 |  |  | 1,367 |
Total investment securities |  | 150 |  |  | $ | 166,051 |  |  | $ | 1,881 |  |  | $ | 12,265 |  |  | $ | 385 |  |  | $ | 178,316 |  |  | $ | 2,266 |
|  | 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 |  | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |  |  | $ | — |
Municipal and other tax-exempt |  | 19 |  |  | 12,765 |  |  | 18 |  |  | 4,802 |  |  | 265 |  |  | 17,567 |  |  | 283 |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U. S. government agencies: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FNMA |  | 113 |  |  | 1,203,041 |  |  | 9,618 |  |  | 824,029 |  |  | 25,919 |  |  | 2,027,070 |  |  | 35,537 |
FHLMC |  | 69 |  |  | 863,778 |  |  | 7,297 |  |  | 385,816 |  |  | 10,813 |  |  | 1,249,594 |  |  | 18,110 |
GNMA |  | 27 |  |  | 201,887 |  |  | 1,452 |  |  | 248,742 |  |  | 7,201 |  |  | 450,629 |  |  | 8,653 |
Total U.S. government agencies |  | 209 |  |  | 2,268,706 |  |  | 18,367 |  |  | 1,458,587 |  |  | 43,933 |  |  | 3,727,293 |  |  | 62,300 |
Private issue1 |  | 8 |  |  | 5,898 |  |  | 391 |  |  | — |  |  | — |  |  | 5,898 |  |  | 391 |
Total residential mortgage-backed securities |  | 217 |  |  | 2,274,604 |  |  | 18,758 |  |  | 1,458,587 |  |  | 43,933 |  |  | 3,733,191 |  |  | 62,691 |
Commercial mortgage-backed securities guaranteed by U.S. government agencies |  | 185 |  |  | 1,465,703 |  |  | 11,824 |  |  | 652,296 |  |  | 14,063 |  |  | 2,117,999 |  |  | 25,887 |
Other debt securities |  | 2 |  |  | 19,959 |  |  | 41 |  |  | 472 |  |  | 28 |  |  | 20,431 |  |  | 69 |
Perpetual preferred stocks |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Equity securities and mutual funds |  | 111 |  |  | 911 |  |  | 7 |  |  | 2,203 |  |  | 79 |  |  | 3,114 |  |  | 86 |
Total available for sale securities |  | 534 |  |  | $ | 3,773,942 |  |  | $ | 30,648 |  |  | $ | 2,118,360 |  |  | $ | 58,368 |  |  | $ | 5,892,302 |  |  | $ | 89,016 |
1 | Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income.
Temporarily Impaired Securities as of June 30, 2017 (In thousands)
|  | 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 |  | 82 |  |  | $ | 111,078 |  |  | $ | 149 |  |  | $ | 3,000 |  |  | $ | 79 |  |  | $ | 114,078 |  |  | $ | 228 |
U.S. government agency residential mortgage-backed securities |  | 1 |  |  | 3,810 |  |  | 61 |  |  | — |  |  | — |  |  | 3,810 |  |  | 61 |
Other debt securities |  | 22 |  |  | 8,384 |  |  | 554 |  |  | — |  |  | — |  |  | 8,384 |  |  | 554 |
Total investment securities |  | 105 |  |  | $ | 123,272 |  |  | $ | 764 |  |  | $ | 3,000 |  |  | $ | 79 |  |  | $ | 126,272 |  |  | $ | 843 |
|  | 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 |  |  | $ | 997 |  |  | $ | 2 |  |  | $ | — |  |  | $ | — |  |  | $ | 997 |  |  | $ | 2 |
Municipal and other tax-exempt |  | 13 |  |  | 1,957 |  |  | 1 |  |  | 4,655 |  |  | 412 |  |  | 6,612 |  |  | 413 |
Residential mortgage-backed securities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
U. S. government agencies: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
FNMA |  | 75 |  |  | 1,381,687 |  |  | 20,288 |  |  | 87,371 |  |  | 1,314 |  |  | 1,469,058 |  |  | 21,602 |
FHLMC |  | 42 |  |  | 731,853 |  |  | 7,213 |  |  | 16,388 |  |  | 476 |  |  | 748,241 |  |  | 7,689 |
GNMA |  | 21 |  |  | 291,806 |  |  | 3,766 |  |  | 76,605 |  |  | 1,596 |  |  | 368,411 |  |  | 5,362 |
Other |  | 1 |  |  | 19,957 |  |  | 43 |  |  | — |  |  | — |  |  | 19,957 |  |  | 43 |
Total U.S. government agencies |  | 139 |  |  | 2,425,303 |  |  | 31,310 |  |  | 180,364 |  |  | 3,386 |  |  | 2,605,667 |  |  | 34,696 |
Private issue1 |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Total residential mortgage-backed securities |  | 139 |  |  | 2,425,303 |  |  | 31,310 |  |  | 180,364 |  |  | 3,386 |  |  | 2,605,667 |  |  | 34,696 |
Commercial mortgage-backed securities guaranteed by U.S. government agencies |  | 121 |  |  | 1,388,406 |  |  | 12,690 |  |  | 78,828 |  |  | 1,587 |  |  | 1,467,234 |  |  | 14,277 |
Other debt securities |  | 2 |  |  | — |  |  | — |  |  | 4,152 |  |  | 248 |  |  | 4,152 |  |  | 248 |
Perpetual preferred stocks |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Equity securities and mutual funds |  | 91 |  |  | 1,668 |  |  | 22 |  |  | 887 |  |  | 41 |  |  | 2,555 |  |  | 63 |
Total available for sale securities |  | 367 |  |  | $ | 3,818,331 |  |  | $ | 44,025 |  |  | $ | 268,886 |  |  | $ | 5,674 |  |  | $ | 4,087,217 |  |  | $ | 49,699 |
1 | Includes securities for which an unrealized loss remains in AOCI after an other-than-temporary credit loss has been recognized in income.
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):
|  | June 30, 2018 |  | December 31, 2017 |  | June 30, 2017
|  | Fair Value |  | Net Unrealized Gain (Loss) |  | Fair Value |  | Net Unrealized Gain (Loss) |  | Fair Value |  | Net Unrealized Gain (Loss)
U.S. government agency residential mortgage-backed securities |  | $ | 482,227 |  |  | $ | (5,509 | ) |  | $ | 755,054 |  |  | $ | (1,877 | ) |  | $ | 445,169 |  |  | $ | 1,247 |
Schedule of Restricted Equity Securities [Table Text Block] |
| June 30, 2018 |  | Dec. 31, 2017 |  | June 30, 2017
Federal Reserve stock | $ | 41,178 |  |  | $ | 40,746 |  |  | $ | 36,676 |
Federal Home Loan Bank stock | 306,543 |  |  | 279,200 |  |  | 274,113 |
Other | — |  |  | 243 |  |  | 244 |
Total | $ | 347,721 |  |  | $ | 320,189 |  |  | $ | 311,033 |

X
- Definition Fair Value Option Securities [Table Text Block] + References No definition available. + Details
Name: | bokf_FairValueOptionSecuritiesTableTextBlock
Namespace Prefix: | bokf_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Securities Pledged As Collateral [Table Text Block] + References No definition available. + Details
Name: | bokf_SecuritiesPledgedAsCollateralTableTextBlock
Namespace Prefix: | bokf_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62557-112803 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27198-111563 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62586-112803 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of all investments in certain debt and equity securities for which the entity has the positive intent and ability to hold until maturity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27405-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62586-112803 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=6435544&loc=d3e41834-113960 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 320 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62557-112803 + Details
Name: | us-gaap_HeldToMaturitySecuritiesTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_MarketableSecuritiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition A tabular disclosure of (a) the aggregate carrying amount of all cost-method investments; (b) the aggregate carrying amount of cost-method investments that the investor did not evaluate for impairment for cost-method investments. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 325 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=75025870&loc=d3e40691-111596 + Details
Name: | us-gaap_ScheduleOfCostMethodInvestmentsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition For all investments in an unrealized loss position, including those for which other-than-temporary impairments have not been recognized in earnings (including investments for which a portion of an other-than-temporary impairment has been recognized in other comprehensive income), a tabular disclosure of the aggregate related fair value of investments with unrealized losses and the aggregate amount of unrealized losses (that is, the amount by which amortized cost basis exceeds fair value). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_ScheduleOfUnrealizedLossOnInvestmentsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of investments in trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (c),(e) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26626-111562 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_TradingSecuritiesAndCertainTradingAssetsTextBlock
Namespace Prefix: | us-gaap_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration