Reportable Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	$ 984,867	$ 841,701	$ 747,228
Net interest revenue (expense) from internal sources	0	0	0
Net interest and dividend revenue	984,867	841,701	747,228
Provision for credit losses	8,000	(7,000)	65,000
Net interest and dividend revenue after provision for credit losses	976,867	848,701	682,228
Other operating revenue	616,784	695,094	674,020
Other operating expense	1,028,166	1,025,517	1,017,590
Net direct contribution	565,485	518,278	338,658
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	565,485	518,278	338,658
Federal and state income taxes	119,061	182,593	106,377
Net income	446,424	335,685	232,281
Net income (loss) attributable to non-controlling interests	778	1,041	(387)
Net income attributable to BOK Financial Corp. shareholders	445,646	334,644	232,668
Average assets	34,937,530	32,947,494	32,278,402
Operating Segments [Member] | Commercial [Member]
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	726,856	618,325	501,042
Net interest revenue (expense) from internal sources	(156,254)	(89,106)	(62,655)
Net interest and dividend revenue	570,602	529,219	438,387
Provision for credit losses	30,358	13,877	32,961
Net interest and dividend revenue after provision for credit losses	540,244	515,342	405,426
Other operating revenue	162,701	208,404	198,902
Other operating expense	192,811	228,119	217,993
Net direct contribution	510,134	495,627	386,335
Gain (loss) on financial instruments, net	26	52	10
Change in fair value of mortgage servicing rights	0	0	0
Gain (loss) on repossessed assets, net	(6,532)	(2,681)	669
Corporate expense allocations	45,818	34,253	36,134
Net income before taxes	457,810	458,745	350,880
Federal and state income taxes	121,434	188,241	146,740
Net income	336,376	270,504	204,140
Net income (loss) attributable to non-controlling interests	0	0	0
Net income attributable to BOK Financial Corp. shareholders	336,376	270,504	204,140
Average assets	18,431,411	17,730,654	17,175,325
Operating Segments [Member] | Consumer [Member]
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	83,231	84,286	77,283
Net interest revenue (expense) from internal sources	73,448	53,916	43,156
Net interest and dividend revenue	156,679	138,202	120,439
Provision for credit losses	5,143	4,786	4,925
Net interest and dividend revenue after provision for credit losses	151,536	133,416	115,514
Other operating revenue	178,123	184,878	216,285
Other operating expense	210,187	221,679	247,478
Net direct contribution	119,472	96,615	84,321
Gain (loss) on financial instruments, net	(25,021)	(2,054)	(26,252)
Change in fair value of mortgage servicing rights	4,668	172	(2,193)
Gain (loss) on repossessed assets, net	247	223	979
Corporate expense allocations	63,700	67,320	65,567
Net income before taxes	35,666	27,636	(8,712)
Federal and state income taxes	9,085	10,750	(3,389)
Net income	26,581	16,886	(5,323)
Net income (loss) attributable to non-controlling interests	0	0	0
Net income attributable to BOK Financial Corp. shareholders	26,581	16,886	(5,323)
Average assets	8,303,262	8,544,117	8,254,666
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	81,527	45,024	33,006
Net interest revenue (expense) from internal sources	31,505	38,344	29,043
Net interest and dividend revenue	113,032	83,368	62,049
Provision for credit losses	(288)	(696)	(801)
Net interest and dividend revenue after provision for credit losses	113,320	84,064	62,850
Other operating revenue	296,369	301,434	283,222
Other operating expense	248,959	246,626	250,995
Net direct contribution	160,730	138,872	95,077
Gain (loss) on financial instruments, net	7	0	(42)
Change in fair value of mortgage servicing rights	0	0	0
Gain (loss) on repossessed assets, net	0	387	0
Corporate expense allocations	44,190	40,562	42,378
Net income before taxes	116,547	98,697	52,657
Federal and state income taxes	30,003	38,848	20,976
Net income	86,544	59,849	31,681
Net income (loss) attributable to non-controlling interests	0	0	0
Net income attributable to BOK Financial Corp. shareholders	86,544	59,849	31,681
Average assets	8,446,006	7,072,622	7,373,080
Funds Management and Other [Member]
Segment Reporting Information [Line Items]
Net interest and dividend revenue from external sources	93,253	94,066	135,897
Net interest revenue (expense) from internal sources	51,301	(3,154)	(9,544)
Net interest and dividend revenue	144,554	90,912	126,353
Provision for credit losses	(27,213)	(24,967)	27,915
Net interest and dividend revenue after provision for credit losses	171,767	115,879	98,438
Other operating revenue	(20,409)	378	(24,389)
Other operating expense	376,209	329,093	301,124
Net direct contribution	(224,851)	(212,836)	(227,075)
Gain (loss) on financial instruments, net	24,988	2,002	26,284
Change in fair value of mortgage servicing rights	(4,668)	(172)	2,193
Gain (loss) on repossessed assets, net	6,285	2,071	(1,648)
Corporate expense allocations	(153,708)	(142,135)	(144,079)
Net income before taxes	(44,538)	(66,800)	(56,167)
Federal and state income taxes	(41,461)	(55,246)	(57,950)
Net income	(3,077)	(11,554)	1,783
Net income (loss) attributable to non-controlling interests	778	1,041	(387)
Net income attributable to BOK Financial Corp. shareholders	(3,855)	(12,595)	2,170
Average assets	$ (243,149)	$ (399,899)	$ (524,669)