Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
NIR (expense) from external sources	$ 218,452	$ 187,846	$ 624,838	$ 553,030
NIR (expense) from internal sources	0	0	0	0
Net interest revenue	218,452	187,846	624,838	553,030
Provision for credit losses	0	10,000	0	65,000
Net interest revenue after provision for credit losses	218,452	177,846	624,838	488,030
Other operating revenue	175,710	187,310	528,258	530,266
Other operating expense	265,934	258,088	761,530	752,043
Net direct contribution	128,228	107,068	391,566	266,253
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	128,228	107,068	391,566	266,253
Federal and state income taxes	42,438	31,956	128,246	83,881
Net income	85,790	75,112	263,320	182,372
Net income (loss) attributable to non-controlling interests	141	835	1,168	(270)
Net income attributable to BOK Financial Corp. shareholders	85,649	74,277	262,152	182,642
Average assets	33,008,170	32,646,473	32,777,438	32,049,183
Operating Segments [Member] | Commercial [Member]
Segment Reporting Information [Line Items]
NIR (expense) from external sources	157,080	123,599	435,946	358,713
NIR (expense) from internal sources	(24,173)	(15,052)	(61,803)	(44,259)
Net interest revenue	132,907	108,547	374,143	314,454
Provision for credit losses	3,217	5,601	2,983	34,024
Net interest revenue after provision for credit losses	129,690	102,946	371,160	280,430
Other operating revenue	54,091	49,642	156,139	146,248
Other operating expense	56,952	53,375	168,517	162,039
Net direct contribution	126,829	99,213	358,782	264,639
Gain (loss) on financial instruments, net	4	0	46	0
Change in fair value of mortgage servicing rights	0	0	0	0
Gain (loss) on repossessed assets, net	(4,126)	1,486	(2,728)	806
Corporate expense allocations	8,650	9,054	26,144	26,681
Net income before taxes	114,057	91,645	329,956	238,764
Federal and state income taxes	44,368	35,650	128,353	92,879
Net income	69,689	55,995	201,603	145,885
Net income (loss) attributable to non-controlling interests	0	0	0	0
Net income attributable to BOK Financial Corp. shareholders	69,689	55,995	201,603	145,885
Average assets	17,558,390	16,934,587	17,525,658	16,958,999
Operating Segments [Member] | Consumer [Member]
Segment Reporting Information [Line Items]
NIR (expense) from external sources	25,576	22,098	70,208	65,897
NIR (expense) from internal sources	12,213	9,263	35,002	27,492
Net interest revenue	37,789	31,361	105,210	93,389
Provision for credit losses	1,315	1,157	3,512	4,177
Net interest revenue after provision for credit losses	36,474	30,204	101,698	89,212
Other operating revenue	47,033	60,603	146,440	172,072
Other operating expense	56,785	60,964	166,027	179,487
Net direct contribution	26,722	29,843	82,111	81,797
Gain (loss) on financial instruments, net	1,686	(1,087)	5,242	30,539
Change in fair value of mortgage servicing rights	(639)	2,327	(5,726)	(41,944)
Gain (loss) on repossessed assets, net	292	161	253	566
Corporate expense allocations	17,039	16,905	50,947	49,513
Net income before taxes	11,022	14,339	30,933	21,445
Federal and state income taxes	4,288	5,578	12,033	8,342
Net income	6,734	8,761	18,900	13,103
Net income (loss) attributable to non-controlling interests	0	0	0	0
Net income attributable to BOK Financial Corp. shareholders	6,734	8,761	18,900	13,103
Average assets	9,115,319	8,827,816	8,871,470	8,763,564
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
NIR (expense) from external sources	11,169	9,274	33,130	21,620
NIR (expense) from internal sources	9,604	7,401	28,784	22,258
Net interest revenue	20,773	16,675	61,914	43,878
Provision for credit losses	(623)	(89)	(676)	(479)
Net interest revenue after provision for credit losses	21,396	16,764	62,590	44,357
Other operating revenue	75,707	73,523	225,434	218,042
Other operating expense	61,791	64,426	182,816	186,524
Net direct contribution	35,312	25,861	105,208	75,875
Gain (loss) on financial instruments, net	0	(42)	0	(42)
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	9,819	10,912	30,438	31,864
Net income before taxes	25,493	14,907	74,770	43,969
Federal and state income taxes	9,917	5,799	29,086	17,104
Net income	15,576	9,108	45,684	26,865
Net income (loss) attributable to non-controlling interests	0	0	0	0
Net income attributable to BOK Financial Corp. shareholders	15,576	9,108	45,684	26,865
Average assets	6,992,021	6,413,735	6,971,369	5,916,545
Funds Management and Other [Member]
Segment Reporting Information [Line Items]
NIR (expense) from external sources	24,627	32,875	85,554	106,800
NIR (expense) from internal sources	2,356	(1,612)	(1,983)	(5,491)
Net interest revenue	26,983	31,263	83,571	101,309
Provision for credit losses	(3,909)	3,331	(5,819)	27,278
Net interest revenue after provision for credit losses	30,892	27,932	89,390	74,031
Other operating revenue	(1,121)	3,542	245	(6,096)
Other operating expense	90,406	79,323	244,170	223,993
Net direct contribution	(60,635)	(47,849)	(154,535)	(156,058)
Gain (loss) on financial instruments, net	(1,690)	1,129	(5,288)	(30,497)
Change in fair value of mortgage servicing rights	639	(2,327)	5,726	41,944
Gain (loss) on repossessed assets, net	3,834	(1,647)	2,475	(1,372)
Corporate expense allocations	(35,508)	(36,871)	(107,529)	(108,058)
Net income before taxes	(22,344)	(13,823)	(44,093)	(37,925)
Federal and state income taxes	(16,135)	(15,071)	(41,226)	(34,444)
Net income	(6,209)	1,248	(2,867)	(3,481)
Net income (loss) attributable to non-controlling interests	141	835	1,168	(270)
Net income attributable to BOK Financial Corp. shareholders	(6,350)	413	(4,035)	(3,211)
Average assets	$ (657,560)	$ 470,335	$ (591,059)	$ 410,075