Shareholders' Equity Regulatory Capital (Details) - USD ($) $ in Thousands		Dec. 31, 2019	Dec. 31, 2018
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	[1]	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		$ 3,608,821	$ 3,356,524
Common Equity Tier 1 Capital to Risk Weighted Assets		11.39%	10.92%
Tier I Capital (to Risk Weighted Assets) [Abstract]
Minimum Capital Requirement, Tier 1 Capital to Risk Weighted Assets		6.00%	6.00%
Capital Conservation Buffer, Tier 1 Capital to Risk Weighted Assets	[1]	2.50%	2.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Tier One to Risk Weighted Assets		8.50%	8.50%
Tier 1 Capital		$ 3,608,821	$ 3,356,524
Tier 1 Capital to Risk Weighted Assets		11.39%	10.92%
Total Capital (to Risk Weighted Assets) [Abstract]
Minimum Capital Requirement, Total Capital to Risk Weighted Assets		8.00%	8.00%
Capital Conservation Buffer, Total Capital to Risk Weighted Assets	[1]	2.50%	2.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Total Capital to Risk Weighted Assets		10.50%	10.50%
Total Capital		$ 4,097,087	$ 3,841,684
Total Capital to Risk Weighted Assets		12.94%	12.50%
Tier 1 Capital (to Average Assets) [Abstract]
Minimum Capital Requirement, Tier 1 Capital to Average Assets		4.00%	4.00%
Minimum Capital Requirements Including Capital Conservation Buffer, Tier 1 Capital to Average Assets		4.00%	4.00%
Tier 1 Leverage Capital		$ 3,608,820	$ 3,356,524
Tier 1 Capital to Average Assets		8.40%	8.96%
Phased in Capital Conservation Buffer		2.50%	1.875%
Fully Phased In Capital Conservation Buffer		2.50%
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		$ 3,414,446	$ 2,894,119
Common Equity Tier 1 Capital to Risk Weighted Assets		10.90%	10.50%
Tier I Capital (to Risk Weighted Assets) [Abstract]
Tier I Capital Ratio Required to be Well Capitalized		8.00%	8.00%
Minimum Capital Requirement, Tier 1 Capital to Risk Weighted Assets		6.00%	6.00%
Minimum Capital Requirement Including Capital Conservation Buffer, Tier One to Risk Weighted Assets		6.00%	6.00%
Tier 1 Capital		$ 3,414,446	$ 2,894,119
Tier 1 Capital to Risk Weighted Assets		10.90%	10.50%
Total Capital (to Risk Weighted Assets) [Abstract]
Total Capital Ratio Required to be Well Capitalized		10.00%	10.00%
Minimum Capital Requirement, Total Capital to Risk Weighted Assets		8.00%	8.00%
Minimum Capital Requirement Including Capital Conservation Buffer, Total Capital to Risk Weighted Assets		8.00%	8.00%
Total Capital		$ 3,692,010	$ 3,103,366
Total Capital to Risk Weighted Assets		11.79%	11.26%
Tier 1 Capital (to Average Assets) [Abstract]
Leverage Ratio Required to be Well Capitalized		5.00%	5.00%
Minimum Capital Requirement, Tier 1 Capital to Average Assets		4.00%	4.00%
Minimum Capital Requirements Including Capital Conservation Buffer, Tier 1 Capital to Average Assets		4.00%	4.00%
Tier 1 Leverage Capital		$ 3,414,446	$ 2,894,119
Tier 1 Capital to Average Assets		7.98%	8.56%
Subsidiaries [Member] | CoBiz Bank [Member]
Common Equity Tier 1 Capital [Abstract]
Common Equity Tier 1 Capital Ratio Required to be Well Capitalized	[2]	6.50%	6.50%
Minimum Capital Requirements, Common Equity Tier 1 to Risk Weighted Assets	[2]	4.50%	4.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Common Equity Tier 1 to Risk Weighted Assets	[2]	4.50%	4.50%
Common Equity Tier 1 Capital	[2]	$ 0	$ 317,944
Common Equity Tier 1 Capital to Risk Weighted Assets	[2]	0.00%	10.65%
Tier I Capital (to Risk Weighted Assets) [Abstract]
Tier I Capital Ratio Required to be Well Capitalized	[2]	8.00%	8.00%
Minimum Capital Requirement, Tier 1 Capital to Risk Weighted Assets	[2]	6.00%	6.00%
Minimum Capital Requirement Including Capital Conservation Buffer, Tier One to Risk Weighted Assets	[2]	6.00%	6.00%
Tier 1 Capital	[2]	$ 0	$ 317,944
Tier 1 Capital to Risk Weighted Assets	[2]	0.00%	10.65%
Total Capital (to Risk Weighted Assets) [Abstract]
Total Capital Ratio Required to be Well Capitalized	[2]	10.00%	10.00%
Minimum Capital Requirement, Total Capital to Risk Weighted Assets	[2]	8.00%	8.00%
Minimum Capital Requirement Including Capital Conservation Buffer, Total Capital to Risk Weighted Assets	[2]	8.00%	8.00%
Total Capital	[2]	$ 0	$ 382,944
Total Capital to Risk Weighted Assets	[2]	0.00%	12.83%
Tier 1 Capital (to Average Assets) [Abstract]
Leverage Ratio Required to be Well Capitalized	[2]	5.00%	5.00%
Minimum Capital Requirement, Tier 1 Capital to Average Assets	[2]	4.00%	4.00%
Minimum Capital Requirements Including Capital Conservation Buffer, Tier 1 Capital to Average Assets	[2]	4.00%	4.00%
Tier 1 Leverage Capital	[2]	$ 0	$ 317,944
Tier 1 Capital to Average Assets	[2]	0.00%	8.25%

[1] Capital conservation buffer was effective January 1, 2016 and phased in through 2019. The phased in capital conservation buffer was 2.50% at December 31, 2019 and 1.875% at December 31, 2018. The fully phased in requirement of 2.50% is included in the table above.

[2] CoBiz Bank was acquired by BOK Financial effective October 1, 2018 and merged into BOKF, NA during the first quarter of 2019.