Parent Company Only Financial Statements Parent Company Only Financial Statements, Condensed Income Statements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Income Statements, Captions [Line Items]
Interest expense	$ 419,079	$ 243,559	$ 131,050
Other operating expense	1,132,381	1,028,166	1,025,517
Other gains (losses), net	(9,351)	2,265	(11,434)
Federal and state income taxes	130,183	119,061	182,593
Net income attributable to BOK Financial Corp. shareholders	500,758	445,646	334,644
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Total revenue	354,368	439,825	168,585
Interest expense	15,113	9,827	8,239
Other operating expense	2,352	12,110	2,014
Total expense	17,465	21,937	10,253
Net income before taxes, other losses, net, and equity in undistributed income of subsidiaries	336,903	417,888	158,332
Other gains (losses), net	3,310	(3,921)	0
Net income before taxes, other losses, net, and equity in undistributed income of subsidiaries	340,213	413,967	158,332
Federal and state income taxes	(4,516)	(7,078)	(4,305)
Net income before equity in undistributed income of subsidiaries	344,729	421,045	162,637
Equity in undistributed income of bank subsidiaries	166,797	37,515	181,552
Equity in undistributed income of non-bank subsidiaries	(10,768)	(12,914)	(9,545)
Net income attributable to BOK Financial Corp. shareholders	500,758	445,646	334,644
Parent Company [Member] | Dividends, interest and fees received from bank susidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Total revenue	344,007	426,071	150,149
Parent Company [Member] | Diviidends, interest and fees received from non-bank subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Total revenue	9,325	12,800	17,500
Parent Company [Member] | Other revenue [Member]
Condensed Income Statements, Captions [Line Items]
Total revenue	$ 1,036	$ 954	$ 936