Other Borrowed Funds (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Borrowed Funds [Line Items]
Balance		$ 3,821,361	$ 8,621,328	$ 7,418,714
Average Balance		$ 8,570,959	$ 10,261,592	$ 7,298,229
Rate		0.82%	2.37%	2.03%
Other borrowed funds, Maturities [Abstract]
2021		$ 1,884,974
2022		1,639,735
2023		9,625
2024		625
2025		10,555
Thereafter		275,847
Funds purchased [Member]
Other Borrowed Funds [Line Items]
Balance		$ 769,365	$ 3,390,528	$ 402,450
Rate		0.05%	1.53%	2.34%
Average Balance		$ 2,045,795	$ 2,438,376	$ 419,322
Rate		0.58%	2.08%	1.89%
Maximum Outstanding At Any Month End		$ 3,311,938	$ 3,390,528	$ 949,531
Repurchase agreements [Member]
Other Borrowed Funds [Line Items]
Balance		$ 893,021	$ 427,822	$ 615,961
Rate		0.09%	0.50%	0.36%
Average Balance		$ 1,589,746	$ 399,785	$ 464,582
Rate		0.24%	0.57%	0.28%
Maximum Outstanding At Any Month End		$ 3,230,097	$ 427,822	$ 615,961
Other Borrowings [Member]
Other Borrowed Funds [Line Items]
Balance		1,882,970	4,527,055	6,124,390
Average Balance		$ 4,659,453	$ 7,147,356	$ 6,236,441
Rate		0.88%	2.45%	2.07%
Federal Home Loan Bank advances [Member]
Other Borrowed Funds [Line Items]
Balance		$ 200,000	$ 4,500,000	$ 6,100,000
Rate		0.29%	1.79%	2.65%
Average Balance		$ 3,393,989	$ 7,122,466	$ 6,207,142
Rate		1.00%	2.44%	2.06%
Maximum Outstanding At Any Month End		$ 7,500,000	$ 8,000,000	$ 6,500,000
GNMA repurchase liability [Member]
Other Borrowed Funds [Line Items]
Balance		$ 19,500	$ 15,417	$ 15,552
Rate		4.35%	4.32%	4.43%
Average Balance		$ 42,771	$ 13,746	$ 14,783
Rate		4.18%	4.47%	4.47%
Maximum Outstanding At Any Month End		$ 126,569	$ 19,581	$ 16,529
Federal Reserve Bank Advances
Other Borrowed Funds [Line Items]
Balance		$ 0
Rate		0.00%
Average Balance		$ 42,464
Rate		0.26%
Maximum Outstanding At Any Month End		$ 0
Paycheck protection program liquidity facility
Other Borrowed Funds [Line Items]
Balance		$ 1,635,963
Rate		0.35%
Average Balance		$ 1,152,073
Rate		0.35%
Maximum Outstanding At Any Month End		$ 2,013,414
Other [Member]
Other Borrowed Funds [Line Items]
Balance		$ 27,507	$ 11,638	$ 8,838
Rate		5.24%	5.09%	2.90%
Average Balance		$ 28,156	$ 11,144	$ 14,516
Rate		5.12%	5.30%	2.67%
Maximum Outstanding At Any Month End		$ 49,376	$ 34,676	$ 20,422
Subordinated debentures [Member]
Other Borrowed Funds [Line Items]
Balance	[1]	$ 276,005	$ 275,923	$ 275,913
Rate	[1]	4.72%	5.15%	5.34%
Average Balance	[1]	$ 275,965	$ 276,075	$ 177,884
Rate	[1]	5.05%	5.47%	5.52%
Maximum Outstanding At Any Month End	[1]	$ 276,005	$ 275,923	$ 275,913
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		$ 893,069	431,939
Fair Value		910,885	435,898
Repurchase Liability	[2]	$ 893,021	$ 427,822
Average Rate (in hundredths)		0.09%	0.50%
U.S. government agency mortgage-backed securities [Member] | Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Amortized Cost		$ 893,069	$ 431,939
Fair Value		910,885	435,898
Repurchase Liability	[2]	$ 893,021	$ 427,822
Average Rate (in hundredths)		0.09%	0.50%
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	[2]	$ 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		one day
Number of days to maturity, maximum		ninety days
Subsidiaries [Member] | Repurchase agreements [Member]
Other borrowed funds, Other Disclosures [Abstract]
Number of days to maturity, maximum		ninety 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		$ 381,000
Unused credit available pursuant to the FHLB's collateral policies		8,600,000
Subsidiaries [Member] | BOK Financial Securities, Inc. [Member] | Other [Member]
Other Borrowed Funds [Line Items]
Balance		$ 0	$ 0

[1] Parent Company only.

[2] BOK Financial maintains control over the securities underlying overnight repurchase agreements and generally transfers control over securities underlying longer-term dealer repurchase agreements to the respective counterparty.