Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Net interest revenue from external sources	$ 278,104	$ 285,432	$ 539,464	$ 563,534
Net interest revenue (expense) from internal sources	0	0	0	0
Net interest revenue	278,104	285,432	539,464	563,534
Provision for credit losses	135,321	5,000	229,092	13,000
Net interest revenue after provision for credit losses	142,783	280,432	310,372	550,534
Other operating revenue	232,693	172,065	413,012	329,335
Other operating expense	295,387	277,137	564,011	564,294
Net direct contribution	80,089	175,360	159,373	315,575
Gain (loss) on financial instruments, net	0	0	0	0
Change in fair value of mortgage servicing rights	0	0	0	0
Gain (loss) on repossessed assets, net	0	0	0	0
Corporate expense allocations	0	0	0	0
Net income before taxes	80,089	175,360	159,373	315,575
Federal and state income taxes	15,803	37,580	33,103	67,530
Net income	64,286	137,780	126,270	248,045
Net income (loss) attributable to non-controlling interests	(407)	217	(502)	(130)
Net income attributable to BOK Financial Corp. shareholders	64,693	137,563	126,772	248,175
Average assets	49,757,031	40,844,777	47,738,825	40,261,967
Operating Segments [Member] | Commercial [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	174,314	251,084	376,216	455,293
Net interest revenue (expense) from internal sources	(29,205)	(66,613)	(79,700)	(120,251)
Net interest revenue	145,109	184,471	296,516	335,042
Provision for credit losses	13,762	6,823	30,642	18,069
Net interest revenue after provision for credit losses	131,347	177,648	265,874	316,973
Other operating revenue	47,898	41,611	86,118	79,223
Other operating expense	62,933	63,415	123,685	114,042
Net direct contribution	116,312	155,844	228,307	282,154
Gain (loss) on financial instruments, net	48	20	97	38
Change in fair value of mortgage servicing rights	0	0	0	0
Gain (loss) on repossessed assets, net	191	0	200	(346)
Corporate expense allocations	5,437	10,652	14,342	20,107
Net income before taxes	111,114	145,212	214,262	261,739
Federal and state income taxes	30,122	38,932	58,295	69,938
Net income	80,992	106,280	155,967	191,801
Net income (loss) attributable to non-controlling interests	0	0	0	0
Net income attributable to BOK Financial Corp. shareholders	80,992	106,280	155,967	191,801
Average assets	27,575,652	22,910,724	26,131,814	21,432,513
Operating Segments [Member] | Consumer [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	18,795	25,300	44,671	47,775
Net interest revenue (expense) from internal sources	20,475	27,415	38,531	56,042
Net interest revenue	39,270	52,715	83,202	103,817
Provision for credit losses	535	1,728	1,791	2,813
Net interest revenue after provision for credit losses	38,735	50,987	81,411	101,004
Other operating revenue	67,192	48,811	122,254	91,559
Other operating expense	58,936	57,694	113,729	111,515
Net direct contribution	46,991	42,104	89,936	81,048
Gain (loss) on financial instruments, net	7,356	20,981	94,120	35,078
Change in fair value of mortgage servicing rights	(761)	(29,555)	(89,241)	(50,221)
Gain (loss) on repossessed assets, net	27	92	40	195
Corporate expense allocations	10,812	11,695	21,299	23,595
Net income before taxes	42,801	21,927	73,556	42,505
Federal and state income taxes	10,901	5,585	18,735	10,826
Net income	31,900	16,342	54,821	31,679
Net income (loss) attributable to non-controlling interests	0	0	0	0
Net income attributable to BOK Financial Corp. shareholders	31,900	16,342	54,821	31,679
Average assets	9,920,005	9,212,667	9,885,429	8,794,498
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	34,359	17,222	48,725	38,708
Net interest revenue (expense) from internal sources	(7,479)	9,719	(2,941)	16,489
Net interest revenue	26,880	26,941	45,784	55,197
Provision for credit losses	(89)	(48)	(137)	(167)
Net interest revenue after provision for credit losses	26,969	26,989	45,921	55,364
Other operating revenue	106,674	86,017	204,555	159,431
Other operating expense	80,567	69,452	158,759	130,959
Net direct contribution	53,076	43,554	91,717	83,836
Gain (loss) on financial instruments, net	0	0	7	0
Change in fair value of mortgage servicing rights	0	0	0	0
Gain (loss) on repossessed assets, net	0	0	0	0
Corporate expense allocations	8,204	9,168	16,469	17,528
Net income before taxes	44,872	34,386	75,255	66,308
Federal and state income taxes	11,478	8,842	19,288	17,045
Net income	33,394	25,544	55,967	49,263
Net income (loss) attributable to non-controlling interests	0	0	0	0
Net income attributable to BOK Financial Corp. shareholders	33,394	25,544	55,967	49,263
Average assets	15,721,452	9,849,396	14,222,432	9,590,629
Funds Management and Other [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	50,636	(8,174)	69,852	21,758	[1]
Net interest revenue (expense) from internal sources	16,209	29,479	44,110	47,720	[1]
Net interest revenue	66,845	21,305	113,962	69,478	[1]
Provision for credit losses	121,113	(3,503)	196,796	(7,715)	[1]
Net interest revenue after provision for credit losses	(54,268)	24,808	(82,834)	77,193	[1]
Other operating revenue	10,929	(4,374)	85	(878)	[1]
Other operating expense	92,951	86,576	167,838	207,778	[1]
Net direct contribution	(136,290)	(66,142)	(250,587)	(131,463)	[1]
Gain (loss) on financial instruments, net	(7,404)	(21,001)	(94,224)	(35,116)	[1]
Change in fair value of mortgage servicing rights	761	29,555	89,241	50,221	[1]
Gain (loss) on repossessed assets, net	(218)	(92)	(240)	151	[1]
Corporate expense allocations	(24,453)	(31,515)	(52,110)	(61,230)	[1]
Net income before taxes	(118,698)	(26,165)	(203,700)	(54,977)	[1]
Federal and state income taxes	(36,698)	(15,779)	(63,215)	(30,279)	[1]
Net income	(82,000)	(10,386)	(140,485)	(24,698)	[1]
Net income (loss) attributable to non-controlling interests	(407)	217	(502)	(130)	[1]
Net income attributable to BOK Financial Corp. shareholders	(81,593)	(10,603)	(139,983)	(24,568)	[1]
Average assets	$ (3,460,078)	$ (1,128,010)	$ (2,500,850)	$ 444,327	[1]

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