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.