Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019		Mar. 31, 2018
Segment Reporting Information [Line Items]
Net interest revenue from external sources	$ 278,102		$ 219,736
Net interest revenue (expense) from internal sources	0		0
Net interest revenue	278,102		219,736
Provision for credit losses	8,000		(5,000)
Net interest revenue after provision for credit losses	270,102		224,736
Other operating revenue	157,270		155,989
Other operating expense	287,157		244,430
Net direct contribution	140,215		136,295
Gain (loss) on financial instruments, net	0		0
Change in fair value of mortgage servicing rights	0		0
Gain (loss) on repossessed assets, net	0		0
Corporate expense allocations	0		0
Net income before taxes	140,215		136,295
Federal and state income taxes	29,950		30,948
Net income	110,265		105,347
Net income attributable to non-controlling interests	(347)		(215)
Net income attributable to BOK Financial Corp. shareholders	110,612		105,562
Average assets	39,672,681		33,724,952
Operating Segments [Member] | Commercial [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	204,209		160,414
Net interest revenue (expense) from internal sources	(52,562)		(28,343)
Net interest revenue	151,647		132,071
Provision for credit losses	11,245		627
Net interest revenue after provision for credit losses	140,402		131,444
Other operating revenue	37,612		39,676
Other operating expense	50,177		48,370
Net direct contribution	127,837		122,750
Gain (loss) on financial instruments, net	18		7
Change in fair value of mortgage servicing rights	0		0
Gain (loss) on repossessed assets, net	(346)		(4,166)
Corporate expense allocations	10,148		10,603
Net income before taxes	117,361		107,988
Federal and state income taxes	31,218		28,741
Net income	86,143		79,247
Net income attributable to non-controlling interests	0		0
Net income attributable to BOK Financial Corp. shareholders	86,143		79,247
Average assets	19,330,249		17,793,820
Operating Segments [Member] | Consumer [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	21,595		21,753
Net interest revenue (expense) from internal sources	29,507		15,224
Net interest revenue	51,102		36,977
Provision for credit losses	1,085		1,300
Net interest revenue after provision for credit losses	50,017		35,677
Other operating revenue	42,748		44,947
Other operating expense	53,506		54,695
Net direct contribution	39,259		25,929
Gain (loss) on financial instruments, net	14,097		(23,262)
Change in fair value of mortgage servicing rights	(20,666)		21,206
Gain (loss) on repossessed assets, net	103		(108)
Corporate expense allocations	11,883		11,188
Net income before taxes	20,910		12,577
Federal and state income taxes	5,326		3,203
Net income	15,584		9,374
Net income attributable to non-controlling interests	0		0
Net income attributable to BOK Financial Corp. shareholders	15,584		9,374
Average assets	8,371,683		8,468,101
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	21,486		15,407
Net interest revenue (expense) from internal sources	6,770		9,932
Net interest revenue	28,256		25,339
Provision for credit losses	(119)		(48)
Net interest revenue after provision for credit losses	28,375		25,387
Other operating revenue	73,414		74,766
Other operating expense	61,507		64,942
Net direct contribution	40,282		35,211
Gain (loss) on financial instruments, net	0		0
Change in fair value of mortgage servicing rights	0		0
Gain (loss) on repossessed assets, net	0		0
Corporate expense allocations	8,360		8,815
Net income before taxes	31,922		26,396
Federal and state income taxes	8,203		6,787
Net income	23,719		19,609
Net income attributable to non-controlling interests	0		0
Net income attributable to BOK Financial Corp. shareholders	23,719		19,609
Average assets	9,312,154		8,095,794
Funds Management and Other [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	30,812	[1]	22,162
Net interest revenue (expense) from internal sources	16,285	[1]	3,187
Net interest revenue	47,097	[1]	25,349
Provision for credit losses	(4,211)	[1]	(6,879)
Net interest revenue after provision for credit losses	51,308	[1]	32,228
Other operating revenue	3,496	[1]	(3,400)
Other operating expense	121,967	[1]	76,423
Net direct contribution	(67,163)	[1]	(47,595)
Gain (loss) on financial instruments, net	(14,115)	[1]	23,255
Change in fair value of mortgage servicing rights	20,666	[1]	(21,206)
Gain (loss) on repossessed assets, net	243	[1]	4,274
Corporate expense allocations	(30,391)	[1]	(30,606)
Net income before taxes	(29,978)	[1]	(10,666)
Federal and state income taxes	(14,797)	[1]	(7,783)
Net income	(15,181)	[1]	(2,883)
Net income attributable to non-controlling interests	(347)	[1]	(215)
Net income attributable to BOK Financial Corp. shareholders	(14,834)	[1]	(2,668)
Average assets	$ 2,658,595	[1]	$ (632,763)

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