Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Net interest revenue from external sources	$ 261,360	$ 278,102
Net interest revenue (expense) from internal sources	0	0
Net interest revenue	261,360	278,102
Provision for credit losses	93,771	8,000
Net interest revenue after provision for credit losses	167,589	270,102
Other operating revenue	180,319	157,270
Other operating expense	268,624	287,157
Net direct contribution	79,284	140,215
Gain (loss) on financial instruments, net	0	0
Change in fair value of mortgage servicing rights	0	0
Gain (loss) on repossessed assets, net	0	0
Corporate expense allocations	0	0
Net income before taxes	79,284	140,215
Federal and state income taxes	17,300	29,950
Net income	61,984	110,265
Net income attributable to non-controlling interests	(95)	(347)
Net income attributable to BOK Financial Corp. shareholders	62,079	110,612
Average assets	45,720,618	39,672,681
Operating Segments [Member] | Commercial [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	201,902	204,209
Net interest revenue (expense) from internal sources	(50,495)	(53,638)
Net interest revenue	151,407	150,571
Provision for credit losses	16,880	11,246
Net interest revenue after provision for credit losses	134,527	139,325
Other operating revenue	38,220	37,612
Other operating expense	60,752	50,627
Net direct contribution	111,995	126,310
Gain (loss) on financial instruments, net	49	18
Change in fair value of mortgage servicing rights	0	0
Gain (loss) on repossessed assets, net	9	(346)
Corporate expense allocations	8,905	9,455
Net income before taxes	103,148	116,527
Federal and state income taxes	28,173	31,006
Net income	74,975	85,521
Net income attributable to non-controlling interests	0	0
Net income attributable to BOK Financial Corp. shareholders	74,975	85,521
Average assets	24,687,976	19,937,878
Operating Segments [Member] | Consumer [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	25,876	22,475
Net interest revenue (expense) from internal sources	18,056	28,627
Net interest revenue	43,932	51,102
Provision for credit losses	1,256	1,085
Net interest revenue after provision for credit losses	42,676	50,017
Other operating revenue	55,062	42,748
Other operating expense	54,793	53,821
Net direct contribution	42,945	38,944
Gain (loss) on financial instruments, net	86,764	14,097
Change in fair value of mortgage servicing rights	(88,480)	(20,666)
Gain (loss) on repossessed assets, net	13	103
Corporate expense allocations	10,487	11,900
Net income before taxes	30,755	20,578
Federal and state income taxes	7,834	5,241
Net income	22,921	15,337
Net income attributable to non-controlling interests	0	0
Net income attributable to BOK Financial Corp. shareholders	22,921	15,337
Average assets	9,850,853	8,371,683
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	14,366	21,486
Net interest revenue (expense) from internal sources	4,538	6,770
Net interest revenue	18,904	28,256
Provision for credit losses	(48)	(119)
Net interest revenue after provision for credit losses	18,952	28,375
Other operating revenue	97,881	73,414
Other operating expense	78,192	61,507
Net direct contribution	38,641	40,282
Gain (loss) on financial instruments, net	7	0
Change in fair value of mortgage servicing rights	0	0
Gain (loss) on repossessed assets, net	0	0
Corporate expense allocations	8,265	8,360
Net income before taxes	30,383	31,922
Federal and state income taxes	7,810	8,203
Net income	22,573	23,719
Net income attributable to non-controlling interests	0	0
Net income attributable to BOK Financial Corp. shareholders	22,573	23,719
Average assets	12,723,412	9,328,986
Funds Management and Other [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	19,216	29,932	[1]
Net interest revenue (expense) from internal sources	27,901	18,241	[1]
Net interest revenue	47,117	48,173	[1]
Provision for credit losses	75,683	(4,212)	[1]
Net interest revenue after provision for credit losses	(28,566)	52,385	[1]
Other operating revenue	(10,844)	3,496	[1]
Other operating expense	74,887	121,202	[1]
Net direct contribution	(114,297)	(65,321)	[1]
Gain (loss) on financial instruments, net	(86,820)	(14,115)	[1]
Change in fair value of mortgage servicing rights	88,480	20,666	[1]
Gain (loss) on repossessed assets, net	(22)	243	[1]
Corporate expense allocations	(27,657)	(29,715)	[1]
Net income before taxes	(85,002)	(28,812)	[1]
Federal and state income taxes	(26,517)	(14,500)	[1]
Net income	(58,485)	(14,312)	[1]
Net income attributable to non-controlling interests	(95)	(347)	[1]
Net income attributable to BOK Financial Corp. shareholders	(58,390)	(13,965)	[1]
Average assets	$ (1,541,623)	$ 2,034,134	[1]

[1] ¹ CoBiz operations are included in Funds Management and Other for the first quarter of 2019.