Reportable Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	$ 1,112,879	$ 984,867	$ 841,701
Net interest revenue (expense) from internal sources	0	0	0
Net interest and dividend revenue	1,112,879	984,867	841,701
Provision for credit losses	44,000	8,000	(7,000)
Net interest and dividend revenue after provision for credit losses	1,068,879	976,867	848,701
Other operating revenue	694,370	616,784	695,094
Other operating expense	1,132,381	1,028,166	1,025,517
Net direct contribution	630,868	565,485	518,278
Gain (loss) on financial instruments, net	0	0	0
Change in fair value of mortgage servicing rights	0	0	0
Gain (loss) on repossessed assets, net	0	0	0
Corporate expense allocations	0	0	0
Net income before taxes	630,868	565,485	518,278
Federal and state income taxes	130,183	119,061	182,593
Net income	500,685	446,424	335,685
Net income (loss) attributable to Non-controlling interests	(73)	778	1,041
Net income attributable to BOK Financial Corp. shareholders	500,758	445,646	334,644
Average assets	42,094,347	34,937,530	32,947,494
Operating Segments [Member] | Commercial [Member]
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	919,148	726,855	618,325
Net interest revenue (expense) from internal sources	(242,907)	(159,954)	(92,055)
Net interest and dividend revenue	676,241	566,901	526,270
Provision for credit losses	39,011	30,358	13,877
Net interest and dividend revenue after provision for credit losses	637,230	536,543	512,393
Other operating revenue	170,412	162,701	208,404
Other operating expense	252,459	202,095	235,793
Net direct contribution	555,183	497,149	485,004
Gain (loss) on financial instruments, net	106	26	52
Change in fair value of mortgage servicing rights	0	0	0
Gain (loss) on repossessed assets, net	331	(6,532)	(2,681)
Corporate expense allocations	43,055	36,670	28,060
Net income before taxes	512,565	453,973	454,315
Federal and state income taxes	137,759	120,458	186,518
Net income	374,806	333,515	267,797
Net income (loss) attributable to Non-controlling interests	0	0	0
Net income attributable to BOK Financial Corp. shareholders	374,806	333,515	267,797
Average assets	22,807,589	18,432,035	17,766,027
Operating Segments [Member] | Consumer [Member]
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	99,679	83,231	84,286
Net interest revenue (expense) from internal sources	95,775	73,448	53,916
Net interest and dividend revenue	195,454	156,679	138,202
Provision for credit losses	6,271	5,143	4,786
Net interest and dividend revenue after provision for credit losses	189,183	151,536	133,416
Other operating revenue	187,500	178,123	184,878
Other operating expense	230,916	231,075	241,805
Net direct contribution	145,767	98,584	76,489
Gain (loss) on financial instruments, net	30,375	(25,021)	(2,052)
Change in fair value of mortgage servicing rights	(53,517)	4,668	172
Gain (loss) on repossessed assets, net	496	247	223
Corporate expense allocations	47,169	44,398	49,344
Net income before taxes	75,952	34,080	25,488
Federal and state income taxes	19,346	8,681	9,915
Net income	56,606	25,399	15,573
Net income (loss) attributable to Non-controlling interests	0	0	0
Net income attributable to BOK Financial Corp. shareholders	56,606	25,399	15,573
Average assets	9,301,341	8,303,263	8,544,117
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	61,277	81,528	45,024
Net interest revenue (expense) from internal sources	38,815	31,480	38,344
Net interest and dividend revenue	100,092	113,008	83,368
Provision for credit losses	(308)	(288)	(696)
Net interest and dividend revenue after provision for credit losses	100,400	113,296	84,064
Other operating revenue	341,389	296,369	301,434
Other operating expense	277,267	257,650	254,495
Net direct contribution	164,522	152,015	131,003
Gain (loss) on financial instruments, net	2	7	0
Change in fair value of mortgage servicing rights	0	0	0
Gain (loss) on repossessed assets, net	0	0	387
Corporate expense allocations	36,239	35,920	32,693
Net income before taxes	128,285	116,102	98,697
Federal and state income taxes	32,954	30,075	38,848
Net income	95,331	86,027	59,849
Net income (loss) attributable to Non-controlling interests	0	0	0
Net income attributable to BOK Financial Corp. shareholders	95,331	86,027	59,849
Average assets	10,204,426	8,447,784	7,072,622
Funds Management and Other [Member]
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	32,775	93,253	94,066
Net interest revenue (expense) from internal sources	108,317	55,026	(205)
Net interest and dividend revenue	141,092	148,279	93,861
Provision for credit losses	(974)	(27,213)	(24,967)
Net interest and dividend revenue after provision for credit losses	142,066	175,492	118,828
Other operating revenue	(4,931)	(20,409)	378
Other operating expense	371,739	337,346	293,424
Net direct contribution	(234,604)	(182,263)	(174,218)
Gain (loss) on financial instruments, net	(30,483)	24,988	2,000
Change in fair value of mortgage servicing rights	53,517	(4,668)	(172)
Gain (loss) on repossessed assets, net	(827)	6,285	2,071
Corporate expense allocations	(126,463)	(116,988)	(110,097)
Net income before taxes	(85,934)	(38,670)	(60,222)
Federal and state income taxes	(59,876)	(40,153)	(52,688)
Net income	(26,058)	1,483	(7,534)
Net income (loss) attributable to Non-controlling interests	(73)	778	1,041
Net income attributable to BOK Financial Corp. shareholders	(25,985)	705	(8,575)
Average assets	$ (219,009)	$ (245,552)	$ (435,272)