Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019		Sep. 30, 2018
Segment Reporting Information [Line Items]
Net interest revenue from external sources	$ 279,096	$ 240,883	$ 842,630		$ 699,181
Net interest revenue (expense) from internal sources	0	0	0		0
Net interest revenue	279,096	240,883	842,630		699,181
Provision for credit losses	12,000	4,000	25,000		(1,000)
Net interest revenue after provision for credit losses	267,096	236,883	817,630		700,181
Other operating revenue	186,450	167,941	515,785		480,329
Other operating expense	279,292	252,617	843,586		743,523
Net direct contribution	174,254	152,207	489,829		436,987
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	174,254	152,207	489,829		436,987
Federal and state income taxes	32,396	34,662	99,926		98,940
Net income	141,858	117,545	389,903		338,047
Net income attributable to non-controlling interests	(373)	289	(503)		857
Net income attributable to BOK Financial Corp. shareholders	142,231	117,256	390,406		337,190
Average assets	43,582,110	33,695,817	41,380,843		33,775,495
Operating Segments [Member] | Commercial [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	243,944	187,417	699,239		529,958
Net interest revenue (expense) from internal sources	(63,797)	(42,270)	(181,829)		(107,715)
Net interest revenue	180,147	145,147	517,410		422,243
Provision for credit losses	9,505	8,047	27,574		18,781
Net interest revenue after provision for credit losses	170,642	137,100	489,836		403,462
Other operating revenue	48,832	40,522	128,055		123,245
Other operating expense	68,685	51,039	181,809		148,796
Net direct contribution	150,789	126,583	436,082		377,911
Gain (loss) on financial instruments, net	28	(3)	67		13
Change in fair value of mortgage servicing rights	0	0	0		0
Gain (loss) on repossessed assets, net	802	(1,869)	455		(6,102)
Corporate expense allocations	12,613	9,124	34,146		29,092
Net income before taxes	139,006	115,587	402,458		342,730
Federal and state income taxes	37,433	30,623	107,807		90,943
Net income	101,573	84,964	294,651		251,787
Net income attributable to non-controlling interests	0	0	0		0
Net income attributable to BOK Financial Corp. shareholders	101,573	84,964	294,651		251,787
Average assets	23,973,067	18,499,979	22,288,129		18,124,571
Operating Segments [Member] | Consumer [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	27,580	20,005	75,353		63,504
Net interest revenue (expense) from internal sources	20,882	19,039	76,925		51,811
Net interest revenue	48,462	39,044	152,278		115,315
Provision for credit losses	1,841	1,451	4,654		3,890
Net interest revenue after provision for credit losses	46,621	37,593	147,624		111,425
Other operating revenue	51,221	44,024	142,780		135,291
Other operating expense	59,699	58,482	171,214		174,728
Net direct contribution	38,143	23,135	119,190		71,988
Gain (loss) on financial instruments, net	8,339	(7,229)	43,416		(36,901)
Change in fair value of mortgage servicing rights	(12,593)	5,972	(62,814)		28,901
Gain (loss) on repossessed assets, net	214	(87)	409		(21)
Corporate expense allocations	11,776	11,037	35,369		33,283
Net income before taxes	22,327	10,754	64,832		30,684
Federal and state income taxes	5,687	2,739	16,513		7,816
Net income	16,640	8,015	48,319		22,868
Net income attributable to non-controlling interests	0	0	0		0
Net income attributable to BOK Financial Corp. shareholders	16,640	8,015	48,319		22,868
Average assets	9,827,130	8,323,543	9,142,491		8,381,205
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	12,343	22,509	51,054		56,990
Net interest revenue (expense) from internal sources	10,723	6,267	27,213		26,431
Net interest revenue	23,066	28,776	78,267		83,421
Provision for credit losses	(42)	(84)	(209)		(238)
Net interest revenue after provision for credit losses	23,108	28,860	78,476		83,659
Other operating revenue	89,160	83,357	248,591		228,766
Other operating expense	71,619	62,256	202,579		188,691
Net direct contribution	40,649	49,961	124,488		123,734
Gain (loss) on financial instruments, net	0	7	0		7
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	9,416	11,127	26,943		31,084
Net income before taxes	31,233	38,841	97,545		92,657
Federal and state income taxes	8,027	9,975	25,076		23,824
Net income	23,206	28,866	72,469		68,833
Net income attributable to non-controlling interests	0	0	0		0
Net income attributable to BOK Financial Corp. shareholders	23,206	28,866	72,469		68,833
Average assets	10,392,988	8,498,363	9,861,021		8,364,712
Funds Management and Other [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	(4,771)	10,952	16,984	[1]	48,729
Net interest revenue (expense) from internal sources	32,192	16,964	77,691	[1]	29,473
Net interest revenue	27,421	27,916	94,675	[1]	78,202
Provision for credit losses	696	(5,414)	(7,019)	[1]	(23,433)
Net interest revenue after provision for credit losses	26,725	33,330	101,694	[1]	101,635
Other operating revenue	(2,763)	38	(3,641)	[1]	(6,973)
Other operating expense	79,289	80,840	287,984	[1]	231,308
Net direct contribution	(55,327)	(47,472)	(189,931)	[1]	(136,646)
Gain (loss) on financial instruments, net	(8,367)	7,225	(43,483)	[1]	36,881
Change in fair value of mortgage servicing rights	12,593	(5,972)	62,814	[1]	(28,901)
Gain (loss) on repossessed assets, net	(1,016)	1,956	(864)	[1]	6,123
Corporate expense allocations	(33,805)	(31,288)	(96,458)	[1]	(93,459)
Net income before taxes	(18,312)	(12,975)	(75,006)	[1]	(29,084)
Federal and state income taxes	(18,751)	(8,675)	(49,470)	[1]	(23,643)
Net income	439	(4,300)	(25,536)	[1]	(5,441)
Net income attributable to non-controlling interests	(373)	289	(503)	[1]	857
Net income attributable to BOK Financial Corp. shareholders	812	(4,589)	(25,033)	[1]	(6,298)
Average assets	$ (611,075)	$ (1,626,068)	$ 89,202	[1]	$ (1,094,993)

[1] CoBiz operations are included in Funds Management and Other for the first quarter of 2019 and subsequently allocated to the respective segments in the second quarter of 2019.