Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Net interest revenue from external sources	$ 271,750	$ 279,096	$ 811,214	$ 842,630
Net interest revenue (expense) from internal sources	0	0	0	0
Net interest revenue	271,750	279,096	811,214	842,630
Provision for credit losses	0	12,000	229,092	25,000
Net interest revenue after provision for credit losses	271,750	267,096	582,122	817,630
Other operating revenue	234,159	186,450	647,171	515,785
Other operating expense	301,265	279,292	865,276	843,586
Net direct contribution	204,644	174,254	364,017	489,829
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	204,644	174,254	364,017	489,829
Federal and state income taxes	50,552	32,396	83,655	99,926
Net income	154,092	141,858	280,362	389,903
Net income (loss) attributable to non-controlling interests	58	(373)	(444)	(503)
Net income attributable to BOK Financial Corp. shareholders	154,034	142,231	280,806	390,406
Average assets	48,933,767	43,580,348	48,140,046	41,380,249
Operating Segments [Member] | Commercial [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	173,248	243,944	549,464	699,239
Net interest revenue (expense) from internal sources	(23,302)	(64,984)	(103,002)	(185,235)
Net interest revenue	149,946	178,960	446,462	514,004
Provision for credit losses	22,599	9,505	53,241	27,574
Net interest revenue after provision for credit losses	127,347	169,455	393,221	486,430
Other operating revenue	52,021	48,832	138,139	128,055
Other operating expense	66,846	69,127	190,531	183,169
Net direct contribution	112,522	149,160	340,829	431,316
Gain (loss) on financial instruments, net	38	28	135	67
Change in fair value of mortgage servicing rights	0	0	0	0
Gain (loss) on repossessed assets, net	(4,332)	802	(4,132)	455
Corporate expense allocations	5,172	11,772	19,514	31,880
Net income before taxes	103,056	138,218	317,318	399,958
Federal and state income taxes	27,959	37,232	86,254	107,171
Net income	75,097	100,986	231,064	292,787
Net income (loss) attributable to non-controlling interests	0	0	0	0
Net income attributable to BOK Financial Corp. shareholders	75,097	100,986	231,064	292,787
Average assets	28,000,183	23,973,925	26,759,150	22,288,960
Operating Segments [Member] | Consumer [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	15,821	27,580	60,492	75,353
Net interest revenue (expense) from internal sources	17,309	20,882	55,840	76,925
Net interest revenue	33,130	48,462	116,332	152,278
Provision for credit losses	79	1,841	1,870	4,654
Net interest revenue after provision for credit losses	33,051	46,621	114,462	147,624
Other operating revenue	67,808	51,221	190,062	142,780
Other operating expense	59,839	59,699	173,568	171,214
Net direct contribution	41,020	38,143	130,956	119,190
Gain (loss) on financial instruments, net	1,540	8,339	95,660	43,416
Change in fair value of mortgage servicing rights	3,441	(12,593)	(85,800)	(62,814)
Gain (loss) on repossessed assets, net	41	214	81	409
Corporate expense allocations	10,812	11,776	32,111	35,369
Net income before taxes	35,230	22,327	108,786	64,832
Federal and state income taxes	8,974	5,687	27,709	16,513
Net income	26,256	16,640	81,077	48,319
Net income (loss) attributable to non-controlling interests	0	0	0	0
Net income attributable to BOK Financial Corp. shareholders	26,256	16,640	81,077	48,319
Average assets	9,898,119	9,827,130	9,889,690	9,142,491
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	34,098	12,343	82,823	51,054
Net interest revenue (expense) from internal sources	(11,113)	10,723	(14,054)	27,213
Net interest revenue	22,985	23,066	68,769	78,267
Provision for credit losses	(51)	(42)	(188)	(209)
Net interest revenue after provision for credit losses	23,036	23,108	68,957	78,476
Other operating revenue	111,152	89,160	315,707	248,591
Other operating expense	82,868	71,619	241,627	202,579
Net direct contribution	51,320	40,649	143,037	124,488
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	9,397	9,416	25,866	26,943
Net income before taxes	41,923	31,233	117,178	97,545
Federal and state income taxes	10,711	8,027	29,999	25,076
Net income	31,212	23,206	87,179	72,469
Net income (loss) attributable to non-controlling interests	0	0	0	0
Net income attributable to BOK Financial Corp. shareholders	31,212	23,206	87,179	72,469
Average assets	16,206,522	10,391,225	14,888,623	9,860,427
Funds Management and Other [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	48,583	(4,771)	118,435	16,984	[1]
Net interest revenue (expense) from internal sources	17,106	33,379	61,216	81,097	[1]
Net interest revenue	65,689	28,608	179,651	98,081	[1]
Provision for credit losses	(22,627)	696	174,169	(7,019)	[1]
Net interest revenue after provision for credit losses	88,316	27,912	5,482	105,100	[1]
Other operating revenue	3,178	(2,763)	3,263	(3,641)	[1]
Other operating expense	91,712	78,847	259,550	286,624	[1]
Net direct contribution	(218)	(53,698)	(250,805)	(185,165)	[1]
Gain (loss) on financial instruments, net	(1,578)	(8,367)	(95,802)	(43,483)	[1]
Change in fair value of mortgage servicing rights	(3,441)	12,593	85,800	62,814	[1]
Gain (loss) on repossessed assets, net	4,291	(1,016)	4,051	(864)	[1]
Corporate expense allocations	(25,381)	(32,964)	(77,491)	(94,192)	[1]
Net income before taxes	24,435	(17,524)	(179,265)	(72,506)	[1]
Federal and state income taxes	2,908	(18,550)	(60,307)	(48,834)	[1]
Net income	21,527	1,026	(118,958)	(23,672)	[1]
Net income (loss) attributable to non-controlling interests	58	(373)	(444)	(503)	[1]
Net income attributable to BOK Financial Corp. shareholders	21,469	1,399	(118,514)	(23,169)	[1]
Average assets	$ (5,171,057)	$ (611,932)	$ (3,397,417)	$ 88,371	[1]

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