Parent Company Only Financial Statements Parent Company Only Financial Statements, Condensed Income Statements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Income Statements, Captions [Line Items]
Interest expense	$ 243,559	$ 131,050	$ 81,889
Other operating expense	1,028,166	1,025,517	1,017,590
Other losses, net	(2,731)	11,213	4,947
Federal and state income taxes	119,061	182,593	106,377
Net income attributable to BOK Financial Corp. shareholders	445,646	334,644	232,668
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Total revenue	439,825	168,585	42,772
Interest expense	9,827	8,239	4,182
Other operating expense	12,110	2,014	1,978
Total expense	21,937	10,253	6,160
Net income before taxes, other losses, net, and equity in undistributed income of subsidiaries	417,888	158,332	36,612
Other losses, net	3,921	0	0
Net income before taxes, other losses, net, and equity in undistributed income of subsidiaries	413,967	158,332	36,612
Federal and state income taxes	(7,078)	(4,305)	(1,920)
Net income before equity in undistributed income of subsidiaries	421,045	162,637	38,532
Equity in undistributed income of bank subsidiaries	37,515	181,552	216,120
Equity in undistributed income of non-bank subsidiaries	(12,914)	(9,545)	(21,984)
Net income attributable to BOK Financial Corp. shareholders	445,646	334,644	232,668
Parent Company [Member] | Dividends, interest and fees received from bank susidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Total revenue	426,071	150,149	15,237
Parent Company [Member] | Diviidends, interest and fees received from non-bank subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Total revenue	12,800	17,500	25,923
Parent Company [Member] | Other revenue [Member]
Condensed Income Statements, Captions [Line Items]
Total revenue	$ 954	$ 936	$ 1,612