Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2019		Jun. 30, 2018	Jun. 30, 2019		Jun. 30, 2018
Segment Reporting Information [Line Items]
Net interest revenue from external sources	$ 285,432		$ 238,562	$ 563,534		$ 458,298
Net interest revenue (expense) from internal sources	0		0	0		0
Net interest revenue	285,432		238,562	563,534		458,298
Provision for credit losses	5,000		0	13,000		(5,000)
Net interest revenue after provision for credit losses	280,432		238,562	550,534		463,298
Other operating revenue	172,065		156,399	329,335		312,388
Other operating expense	277,137		246,476	564,294		490,906
Net direct contribution	175,360		148,485	315,575		284,780
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	175,360		148,485	315,575		284,780
Federal and state income taxes	37,580		33,330	67,530		64,278
Net income	137,780		115,155	248,045		220,502
Net income attributable to non-controlling interests	217		783	(130)		568
Net income attributable to BOK Financial Corp. shareholders	137,563		114,372	248,175		219,934
Average assets	40,844,777		33,906,035	40,261,967		33,815,994
Operating Segments [Member] | Commercial [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	251,080		182,127	455,289		342,541
Net interest revenue (expense) from internal sources	(65,470)		(37,102)	(118,031)		(65,445)
Net interest revenue	185,610		145,025	337,258		277,096
Provision for credit losses	6,823		10,108	18,069		10,735
Net interest revenue after provision for credit losses	178,787		134,917	319,189		266,361
Other operating revenue	41,611		43,047	79,223		82,722
Other operating expense	62,947		49,386	113,124		97,756
Net direct contribution	157,451		128,578	285,288		251,327
Gain (loss) on financial instruments, net	20		9	38		16
Change in fair value of mortgage servicing rights	0		0	0		0
Gain (loss) on repossessed assets, net	0		(67)	(346)		(4,232)
Corporate expense allocations	11,384		9,366	21,532		19,969
Net income before taxes	146,087		119,154	263,448		227,142
Federal and state income taxes	39,155		31,577	70,373		60,319
Net income	106,932		87,577	193,075		166,823
Net income attributable to non-controlling interests	0		0	0		0
Net income attributable to BOK Financial Corp. shareholders	106,932		87,577	193,075		166,823
Average assets	22,910,071		18,072,155	21,431,696		17,933,756
Operating Segments [Member] | Consumer [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	24,203		21,747	45,798		43,500
Net interest revenue (expense) from internal sources	28,514		17,548	58,021		32,772
Net interest revenue	52,717		39,295	103,819		76,272
Provision for credit losses	1,728		1,140	2,813		2,441
Net interest revenue after provision for credit losses	50,989		38,155	101,006		73,831
Other operating revenue	48,811		46,320	91,559		91,267
Other operating expense	57,694		61,146	111,515		116,246
Net direct contribution	42,106		23,329	81,050		48,852
Gain (loss) on financial instruments, net	20,981		(6,411)	35,078		(29,672)
Change in fair value of mortgage servicing rights	(29,555)		1,723	(50,221)		22,929
Gain (loss) on repossessed assets, net	92		174	195		66
Corporate expense allocations	11,695		11,042	23,595		22,246
Net income before taxes	21,929		7,773	42,507		19,929
Federal and state income taxes	5,585		1,980	10,826		5,076
Net income	16,344		5,793	31,681		14,853
Net income attributable to non-controlling interests	0		0	0		0
Net income attributable to BOK Financial Corp. shareholders	16,344		5,793	31,681		14,853
Average assets	9,212,667		8,353,558	8,794,498		8,410,513
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	17,224		18,754	38,710		34,161
Net interest revenue (expense) from internal sources	9,719		10,232	16,489		20,164
Net interest revenue	26,943		28,986	55,199		54,325
Provision for credit losses	(48)		(105)	(167)		(153)
Net interest revenue after provision for credit losses	26,991		29,091	55,366		54,478
Other operating revenue	86,017		70,642	159,431		145,409
Other operating expense	69,452		61,491	130,959		124,295
Net direct contribution	43,556		38,242	83,838		75,592
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	9,168		11,142	17,528		22,097
Net income before taxes	34,388		27,100	66,310		53,495
Federal and state income taxes	8,843		6,981	17,046		13,767
Net income	25,545		20,119	49,264		39,728
Net income attributable to non-controlling interests	0		0	0		0
Net income attributable to BOK Financial Corp. shareholders	25,545		20,119	49,264		39,728
Average assets	9,849,396		8,495,557	9,590,629		8,296,780
Funds Management and Other [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	(7,075)	[1]	15,934	23,737	[2]	38,096
Net interest revenue (expense) from internal sources	27,237	[1]	9,322	43,521	[2]	12,509
Net interest revenue	20,162	[1]	25,256	67,258	[2]	50,605
Provision for credit losses	(3,503)	[1]	(11,143)	(7,715)	[2]	(18,023)
Net interest revenue after provision for credit losses	23,665	[1]	36,399	74,973	[2]	68,628
Other operating revenue	(4,374)	[1]	(3,610)	(878)	[2]	(7,010)
Other operating expense	87,044	[1]	74,453	208,696	[2]	152,609
Net direct contribution	(67,753)	[1]	(41,664)	(134,601)	[2]	(90,991)
Gain (loss) on financial instruments, net	(21,001)	[1]	6,402	(35,116)	[2]	29,656
Change in fair value of mortgage servicing rights	29,555	[1]	(1,723)	50,221	[2]	(22,929)
Gain (loss) on repossessed assets, net	(92)	[1]	(107)	151	[2]	4,166
Corporate expense allocations	(32,247)	[1]	(31,550)	(62,655)	[2]	(64,312)
Net income before taxes	(27,044)	[1]	(5,542)	(56,690)	[2]	(15,786)
Federal and state income taxes	(16,003)	[1]	(7,208)	(30,715)	[2]	(14,884)
Net income	(11,041)	[1]	1,666	(25,975)	[2]	(902)
Net income attributable to non-controlling interests	217	[1]	783	(130)	[2]	568
Net income attributable to BOK Financial Corp. shareholders	(11,258)	[1]	883	(25,845)	[2]	(1,470)
Average assets	$ (1,127,357)	[1]	$ (1,015,235)	$ 445,144	[2]	$ (825,055)

[1] CoBiz operations were allocated to the respective segments in the second quarter of 2019.

[2] 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.