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Other Borrowed Funds (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Other Borrowed Funds [Line Items] |  |  |  |
Balance |  | $ 8,621,328 | $ 7,418,714 | $ 5,854,537
Average Balance |  | $ 10,261,592 | $ 7,298,229 | $ 6,559,101
Rate |  | 2.37% | 2.03% | 1.18%
Other borrowed funds, Maturities [Abstract] |  |  |  |
2020 |  | $ 8,335,742 |  |
2021 |  | 1,244 |  |
2022 |  | 575 |  |
2023 |  | 1,454 |  |
2024 |  | 3,599 |  |
Thereafter |  | 278,714 |  |
Funds purchased [Member] |  |  |  |
Other Borrowed Funds [Line Items] |  |  |  |
Balance |  | $ 3,390,528 | $ 402,450 | $ 58,628
Rate |  | 1.53% | 2.34% | 1.00%
Average Balance |  | $ 2,438,376 | $ 419,322 | $ 58,064
Rate |  | 2.08% | 1.89% | 0.73%
Maximum Outstanding At Any Month End |  | $ 3,390,528 | $ 949,531 | $ 80,967
Repurchase agreements [Member] |  |  |  |
Other Borrowed Funds [Line Items] |  |  |  |
Balance |  | $ 427,822 | $ 615,961 | $ 516,335
Rate |  | 0.50% | 0.36% | 0.17%
Average Balance |  | $ 399,785 | $ 464,582 | $ 433,791
Rate |  | 0.57% | 0.28% | 0.10%
Maximum Outstanding At Any Month End |  | $ 427,822 | $ 615,961 | $ 536,094
Other Borrowings [Member] |  |  |  |
Other Borrowed Funds [Line Items] |  |  |  |
Balance |  | 4,527,055 | 6,124,390 | 5,134,897
Average Balance |  | $ 7,147,356 | $ 6,236,441 | $ 5,919,292
Rate |  | 2.45% | 2.07% | 1.15%
Federal Home Loan Bank advances [Member] |  |  |  |
Other Borrowed Funds [Line Items] |  |  |  |
Balance |  | $ 4,500,000 | $ 6,100,000 | $ 5,100,000
Rate |  | 1.79% | 2.65% | 1.47%
Average Balance |  | $ 7,122,466 | $ 6,207,142 | $ 5,882,466
Rate |  | 2.44% | 2.06% | 1.13%
Maximum Outstanding At Any Month End |  | $ 8,000,000 | $ 6,500,000 | $ 6,200,000
GNMA repurchase liability [Member] |  |  |  |
Other Borrowed Funds [Line Items] |  |  |  |
Balance |  | $ 15,417 | $ 15,552 | $ 19,947
Rate |  | 4.32% | 4.43% | 4.22%
Average Balance |  | $ 13,746 | $ 14,783 | $ 20,509
Rate |  | 4.47% | 4.47% | 4.59%
Maximum Outstanding At Any Month End |  | $ 19,581 | $ 16,529 | $ 24,139
Other [Member] |  |  |  |
Other Borrowed Funds [Line Items] |  |  |  |
Balance |  | $ 11,638 | $ 8,838 | $ 14,950
Rate |  | 5.09% | 2.90% | 2.61%
Average Balance |  | $ 11,144 | $ 14,516 | $ 16,317
Rate |  | 5.30% | 2.67% | 3.35%
Maximum Outstanding At Any Month End |  | $ 34,676 | $ 20,422 | $ 18,610
Subordinated debentures [Member] |  |  |  |
Other Borrowed Funds [Line Items] |  |  |  |
Balance | [1] | $ 275,923 | $ 275,913 | $ 144,677
Rate | [1] | 5.15% | 5.34% | 5.60%
Average Balance | [1] | $ 276,075 | $ 177,884 | $ 147,954
Rate | [1] | 5.47% | 5.52% | 5.57%
Maximum Outstanding At Any Month End | [1] | $ 275,923 | $ 275,913 | $ 151,875
Subordinated debentures [Member] | Subordinated debentures, 2016 issuance [Member] |  |  |  |
Other borrowed funds, Other Disclosures [Abstract] |  |  |  |
Amount of debt issuance |  | $ 150,000 |  |
Maturity date |  | Jun. 30, 2056 |  |
Stated interest rate |  | 5.375% |  |
Debt Instrument, Call Date, Earliest |  | Jun. 30, 2021 |  |
Subordinated debentures [Member] | Subordinated debentures-acquired, 2015 Issuance [Member] |  |  |  |
Other borrowed funds, Other Disclosures [Abstract] |  |  |  |
Amount of debt issuance |  | $ 60,000 |  |
Maturity date |  | Jun. 25, 2030 |  |
Interest rate description |  | three-month LIBOR plus 3.17% |  |
Stated interest rate |  | 5.625% |  |
Debt Instrument, Call Date, Earliest |  | Jun. 25, 2025 |  |
Subordinated debentures [Member] | Junior subordinated debentures-acquired, 2003 issuance [Member] |  |  |  |
Other borrowed funds, Other Disclosures [Abstract] |  |  |  |
Amount of debt issuance |  | $ 21,000 |  |
Maturity date |  | Sep. 17, 2033 |  |
Interest rate description |  | three-month LIBOR plus 2.95% |  |
Subordinated debentures [Member] | Junior subordinated debentures-acquired, 2004 issuance [Member] |  |  |  |
Other borrowed funds, Other Disclosures [Abstract] |  |  |  |
Amount of debt issuance |  | $ 31,000 |  |
Maturity date |  | Jul. 23, 2034 |  |
Interest rate description |  | three-month LIBOR plus 2.60% |  |
Subordinated debentures [Member] | Junior subordinated debentures-acquired, 2005 issuance [Member] |  |  |  |
Other borrowed funds, Other Disclosures [Abstract] |  |  |  |
Amount of debt issuance |  | $ 20,000 |  |
Maturity date |  | Sep. 30, 2035 |  |
Interest rate description |  | three-month LIBOR plus 1.45% |  |
U.S. government agency mortgage-backed securities [Member] |  |  |  |
Assets Sold under Agreements to Repurchase [Line Items] |  |  |  |
Amortized Cost |  | $ 431,939 | 636,864 |
Fair Value |  | 435,898 | 628,229 |
Repurchase Liability |  | $ 427,822 | $ 615,961 |
Average Rate (in hundredths) |  | 0.50% | 0.36% |
U.S. government agency mortgage-backed securities [Member] | Overnight [Member] |  |  |  |
Assets Sold under Agreements to Repurchase [Line Items] |  |  |  |
Amortized Cost |  | $ 431,939 | $ 636,864 |
Fair Value |  | 435,898 | 628,229 |
Repurchase Liability |  | $ 427,822 | $ 615,961 |
Average Rate (in hundredths) |  | 0.50% | 0.36% |
U.S. government agency mortgage-backed securities [Member] | Long-term [Member] |  |  |  |
Assets Sold under Agreements to Repurchase [Line Items] |  |  |  |
Amortized Cost |  | $ 0 | $ 0 |
Fair Value |  | 0 | 0 |
Repurchase Liability |  | $ 0 | $ 0 |
Average Rate (in hundredths) |  | 0.00% | 0.00% |
Subsidiaries [Member] | Funds purchased [Member] |  |  |  |
Other borrowed funds, Other Disclosures [Abstract] |  |  |  |
Number of days to maturity, minimum |  | 1 day |  |
Number of days to maturity, maximum |  | 90 days |  |
Subsidiaries [Member] | Repurchase agreements [Member] |  |  |  |
Other borrowed funds, Other Disclosures [Abstract] |  |  |  |
Number of days to maturity, maximum |  | 90 days |  |
Subsidiaries [Member] | Federal Home Loan Bank advances [Member] |  |  |  |
Other borrowed funds, Other Disclosures [Abstract] |  |  |  |
Federal Home Loan Banks, Letters of credit issued to secure public funds |  | $ 661,000 |  |
Unused credit available pursuant to the FHLB's collateral policies |  | 4,900,000 |  |
Subsidiaries [Member] | BOK Financial Securities, Inc. [Member] | Other [Member] |  |  |  |
Other Borrowed Funds [Line Items] |  |  |  |
Balance |  | $ 0 | $ 0 |
[1] | Parent Company only.

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