Parent Company Only Financial Statements Parent Company Only Financial Statements, Condensed Income Statements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Income Statements, Captions [Line Items]
Interest expense	$ 160,556	$ 419,079	$ 243,559
Other operating expense	1,165,937	1,132,381	1,028,166
Other gains (losses), net	7,675	9,351	(2,265)
Federal and state income taxes	128,793	130,183	119,061
Net income attributable to BOK Financial Corp. shareholders	435,030	500,758	445,646
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Total revenue	205,097	354,368	439,825
Interest expense	13,944	15,113	9,827
Other operating expense	2,697	2,352	12,110
Total expense	16,641	17,465	21,937
Net income before taxes, other losses, net, and equity in undistributed income of subsidiaries	188,456	336,903	417,888
Other gains (losses), net	1,465	3,310	(3,921)
Net income before taxes, other losses, net, and equity in undistributed income of subsidiaries	189,921	340,213	413,967
Federal and state income taxes	(4,502)	(4,516)	(7,078)
Net income before equity in undistributed income of subsidiaries	194,423	344,729	421,045
Equity in undistributed income of bank subsidiaries	276,217	166,797	37,515
Equity in undistributed income of non-bank subsidiaries	(35,610)	(10,768)	(12,914)
Net income attributable to BOK Financial Corp. shareholders	435,030	500,758	445,646
Parent Company [Member] | Dividends, interest and fees received from bank susidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Total revenue	179,140	344,007	426,071
Parent Company [Member] | Dividends, interest and fees received from non-bank subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Total revenue	25,050	9,325	12,800
Parent Company [Member] | Other revenue [Member]
Condensed Income Statements, Captions [Line Items]
Total revenue	$ 907	$ 1,036	$ 954