Shareholders' Equity Regulatory Capital (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Common Equity Tier 1 Capital [Abstract]
Minimum Capital Requirements, Common Equity Tier 1 to Risk Weighted Assets	4.50%	4.50%
Capital Conservation Buffer, Common Equity Tier 1 to Risk Weighted Assets	2.50%	2.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Common Equity Tier 1 to Risk Weighted Assets	7.00%	7.00%
Common Equity Tier 1 Capital	$ 3,881,912	$ 3,608,821
Common Equity Tier 1 Capital to Risk Weighted Assets	0.1195	0.1139
Tier I Capital (to Risk Weighted Assets) [Abstract]
Minimum Capital Requirement, Tier 1 Capital to Risk Weighted Assets	0.0600	0.0600
Capital Conservation Buffer, Tier 1 Capital to Risk Weighted Assets	2.50%	2.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Tier One to Risk Weighted Assets	8.50%	8.50%
Tier 1 Capital	$ 3,881,912	$ 3,608,821
Tier 1 Capital to Risk Weighted Assets	0.1195	0.1139
Total Capital (to Risk Weighted Assets) [Abstract]
Minimum Capital Requirement, Total Capital to Risk Weighted Assets	0.0800	0.0800
Capital Conservation Buffer, Total Capital to Risk Weighted Assets	2.50%	2.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Total Capital to Risk Weighted Assets	10.50%	10.50%
Total Capital	$ 4,489,110	$ 4,097,087
Total Capital to Risk Weighted Assets	0.1382	0.1294
Tier 1 Capital (to Average Assets) [Abstract]
Minimum Capital Requirement, Tier 1 Capital to Average Assets	0.0400	0.0400
Minimum Capital Requirements Including Capital Conservation Buffer, Tier 1 Capital to Average Assets	4.00%	4.00%
Tier 1 Leverage Capital	$ 3,881,912	$ 3,608,820
Tier 1 Capital to Average Assets	0.0828	0.0840
Subsidiaries [Member] | BOKF, NA [Member]
Common Equity Tier 1 Capital [Abstract]
Common Equity Tier 1 Capital Ratio Required to be Well Capitalized	6.50%	6.50%
Minimum Capital Requirements, Common Equity Tier 1 to Risk Weighted Assets	4.50%	4.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Common Equity Tier 1 to Risk Weighted Assets	4.50%	4.50%
Common Equity Tier 1 Capital	$ 3,756,950	$ 3,414,446
Common Equity Tier 1 Capital to Risk Weighted Assets	0.1166	0.1090
Tier I Capital (to Risk Weighted Assets) [Abstract]
Tier I Capital Ratio Required to be Well Capitalized	0.0800	0.0800
Minimum Capital Requirement, Tier 1 Capital to Risk Weighted Assets	0.0600	0.0600
Minimum Capital Requirement Including Capital Conservation Buffer, Tier One to Risk Weighted Assets	6.00%	6.00%
Tier 1 Capital	$ 3,756,950	$ 3,414,446
Tier 1 Capital to Risk Weighted Assets	0.1166	0.1090
Total Capital (to Risk Weighted Assets) [Abstract]
Total Capital Ratio Required to be Well Capitalized	0.1000	0.1000
Minimum Capital Requirement, Total Capital to Risk Weighted Assets	0.0800	0.0800
Minimum Capital Requirement Including Capital Conservation Buffer, Total Capital to Risk Weighted Assets	8.00%	8.00%
Total Capital	$ 4,153,347	$ 3,692,010
Total Capital to Risk Weighted Assets	0.1289	0.1179
Tier 1 Capital (to Average Assets) [Abstract]
Leverage Ratio Required to be Well Capitalized	0.0500	0.0500
Minimum Capital Requirement, Tier 1 Capital to Average Assets	0.0400	0.0400
Minimum Capital Requirements Including Capital Conservation Buffer, Tier 1 Capital to Average Assets	4.00%	4.00%
Tier 1 Leverage Capital	$ 3,756,950	$ 3,414,446
Tier 1 Capital to Average Assets	0.0804	0.0798