Other Borrowings (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other Borrowings [Line Items]
Balance		$ 7,418,714	$ 5,854,537	$ 5,717,302
Average Balance		$ 7,298,229	$ 6,559,101	$ 6,901,856
Rate		2.03%	1.18%	0.60%
U.S. government agency mortgage-backed securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Amortized Cost		$ 636,864	$ 525,452
Fair Value		628,229	523,914
Repurchase Liability	[1]	$ 615,961	$ 516,335
Average Rate (in hundredths)		0.36%	0.17%
U.S. government agency mortgage-backed securities [Member] | Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Amortized Cost		$ 636,864	$ 525,452
Fair Value		628,229	523,914
Repurchase Liability	[1]	$ 615,961	$ 516,335
Average Rate (in hundredths)		0.36%	0.17%
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	[1]	$ 0	$ 0
Average Rate (in hundredths)		0.00%	0.00%
Parent Company [Member]
Other Borrowings [Line Items]
Balance		$ 281,120	$ 144,677	$ 152,949
Average Balance		$ 180,544	$ 148,889	$ 77,112
Rate		5.46%	5.65%	5.86%
Other borrowings, Maturities [Abstract]
2019		$ 0
2020		0
2021		0
2022		0
2023		0
Thereafter		281,120
Parent Company [Member] | Other Borrowings [Member]
Other Borrowings [Line Items]
Balance		$ 5,207	$ 0	$ 1,092
Rate		1.57%	0.00%	8.27%
Average Balance		$ 2,660	$ 935	$ 2,073
Rate		1.35%	11.11%	16.11%
Maximum Outstanding At Any Month End		$ 5,335	$ 3,104	$ 3,157
Parent Company [Member] | Subordinated debentures [Member]
Other Borrowings [Line Items]
Balance		$ 275,913	$ 144,677	$ 151,857
Rate		5.34%	5.60%	5.49%
Average Balance		$ 177,884	$ 147,954	$ 75,039
Rate		5.52%	5.57%	5.57%
Maximum Outstanding At Any Month End		$ 275,913	$ 151,875	$ 151,857
Parent Company [Member] | Subordinated debentures, 2016 issuance [Member]
Other borrowings, 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
Parent Company [Member] | Subordinated debentures-acquired, 2015 Issuance [Member]
Other borrowings, 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
Parent Company [Member] | Junior subordinated debentures-acquired, 2003 issuance [Member]
Other borrowings, Other Disclosures [Abstract]
Amount of debt issuance		$ 21,000
Maturity date		Sep. 17, 2033
Interest rate description		three-month LIBOR plus 2.95%
Parent Company [Member] | Junior subordinated debentures-acquired, 2004 issuance [Member]
Other borrowings, Other Disclosures [Abstract]
Amount of debt issuance		$ 31,000
Maturity date		Jul. 23, 2034
Interest rate description		three-month LIBOR plus 2.60%
Parent Company [Member] | Junior subordinated debentures-acquired, 2005 issuance [Member]
Other borrowings, Other Disclosures [Abstract]
Amount of debt issuance		$ 20,000
Maturity date		Sep. 30, 2035
Interest rate description		three-month LIBOR plus 1.45%
Parent Company [Member] | Trust preferred debt [Member]
Other Borrowings [Line Items]
Balance			7,200
Parent Company [Member] | Trust preferred debt, 2003 issuance [Member]
Other Borrowings [Line Items]
Balance			$ 3,100
Other borrowings, Other Disclosures [Abstract]
Interest rate description			three-month LIBOR plus 2.95%
Parent Company [Member] | Trust preferred debt, 2006 issuance [Member]
Other Borrowings [Line Items]
Balance			$ 4,100
Other borrowings, Other Disclosures [Abstract]
Interest rate description			three-month LIBOR plus 1.82%
Subsidiaries [Member] | BOKF, NA [Member]
Other Borrowings [Line Items]
Balance		$ 7,137,594	$ 5,709,860	5,564,353
Average Balance		$ 7,117,685	$ 6,410,212	$ 6,824,744
Rate		1.94%	1.07%	0.54%
Other borrowings, Maturities [Abstract]
2019		$ 7,134,538
2020		575
2021		575
2022		575
2023		625
Thereafter		706
Subsidiaries [Member] | BOKF, NA [Member] | Funds purchased [Member]
Other Borrowings [Line Items]
Balance		$ 402,450	$ 58,628	$ 57,929
Rate		2.34%	1.00%	0.38%
Average Balance		$ 419,322	$ 58,064	$ 78,222
Rate		1.89%	0.73%	0.24%
Maximum Outstanding At Any Month End		$ 949,531	$ 80,967	$ 567,103
Other borrowings, Other Disclosures [Abstract]
Number of days to maturity, minimum		1 day
Number of days to maturity, maximum		90 days
Subsidiaries [Member] | BOKF, NA [Member] | Repurchase agreements [Member]
Other Borrowings [Line Items]
Balance		$ 615,961	$ 516,335	$ 668,661
Rate		0.36%	0.17%	0.02%
Average Balance		$ 464,582	$ 433,791	$ 589,145
Rate		0.28%	0.10%	0.04%
Maximum Outstanding At Any Month End		$ 615,961	$ 536,094	$ 668,661
Other borrowings, Other Disclosures [Abstract]
Number of days to maturity, maximum		90 days
Subsidiaries [Member] | BOKF, NA [Member] | Other Borrowings [Member]
Other Borrowings [Line Items]
Balance		$ 6,119,183	5,134,897	4,837,763
Average Balance		$ 6,233,781	$ 5,918,357	$ 6,016,963
Rate		2.07%	1.14%	0.57%
Subsidiaries [Member] | BOKF, NA [Member] | Federal Home Loan Bank advances [Member]
Other Borrowings [Line Items]
Balance		$ 6,100,000	$ 5,100,000	$ 4,800,000
Rate		2.65%	1.47%	0.72%
Average Balance		$ 6,207,142	$ 5,882,466	$ 5,985,656
Rate		2.06%	1.13%	0.55%
Maximum Outstanding At Any Month End		$ 6,500,000	$ 6,200,000	$ 6,500,000
Other borrowings, Other Disclosures [Abstract]
Federal Home Loan Banks, Letters of credit issued to secure public funds		266,000
Unused credit available pursuant to the FHLB's collateral policies		1,900,000
Subsidiaries [Member] | BOKF, NA [Member] | GNMA repurchase liability [Member]
Other Borrowings [Line Items]
Balance		$ 15,552	$ 19,947	$ 22,471
Rate		4.43%	4.22%	4.26%
Average Balance		$ 14,783	$ 20,509	$ 15,637
Rate		4.47%	4.59%	4.74%
Maximum Outstanding At Any Month End		$ 16,529	$ 24,139	$ 22,471
Subsidiaries [Member] | BOKF, NA [Member] | Other [Member]
Other Borrowings [Line Items]
Balance		$ 3,631	$ 14,950	$ 15,292
Rate		4.80%	2.61%	2.66%
Average Balance		$ 11,856	$ 15,382	$ 15,670
Rate		4.45%	2.38%	2.41%
Maximum Outstanding At Any Month End		$ 15,096	$ 15,506	$ 15,797
Subsidiaries [Member] | BOKF, NA [Member] | Subordinated debentures [Member]
Other Borrowings [Line Items]
Balance		$ 0	$ 0	$ 0
Rate		0.00%	0.00%	0.00%
Average Balance		$ 0	$ 0	$ 140,414
Rate		0.00%	0.00%	1.35%
Maximum Outstanding At Any Month End		$ 0	$ 0	$ 226,434
Subsidiaries [Member] | BOKF, NA [Member] | Subordinated debentures, 2007 issuance [Member]
Other borrowings, Other Disclosures [Abstract]
Amount of debt issuance				$ 250,000
Maturity date				May 15, 2017
Interest rate description				fixed rate of 5.75% through May 14, 2012 and is based on a floating rate of three-month LIBOR plus 0.69% thereafter
Subsidiaries [Member] | BOK Financial Securities, Inc. [Member] | Other [Member]
Other Borrowings [Line Items]
Balance		$ 0

[1] 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.