Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Net interest revenue from external sources	$ 238,562	$ 205,204	$ 458,298	$ 406,386
Net interest revenue (expense) from internal sources	0	0	0	0
Net interest revenue	238,562	205,204	458,298	406,386
Provision for credit losses	0	0	(5,000)	0
Net interest revenue after provision for credit losses	238,562	205,204	463,298	406,386
Other operating revenue	156,399	182,252	312,388	352,548
Other operating expense	246,476	250,885	490,906	495,596
Net direct contribution	148,485	136,571	284,780	263,338
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	148,485	136,571	284,780	263,338
Federal and state income taxes	33,330	47,705	64,278	85,808
Net income	115,155	88,866	220,502	177,530
Net income attributable to non-controlling interests	783	719	568	1,027
Net income attributable to BOK Financial Corp. shareholders	114,372	88,147	219,934	176,503
Average assets	33,906,035	32,368,571	33,815,994	32,660,160
Operating Segments [Member] | Commercial [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	182,127	154,377	342,541	301,753
Net interest revenue (expense) from internal sources	(37,102)	(21,715)	(65,445)	(39,831)
Net interest revenue	145,025	132,662	277,096	261,922
Provision for credit losses	10,108	1,228	10,735	(236)
Net interest revenue after provision for credit losses	134,917	131,434	266,361	262,158
Other operating revenue	43,047	56,353	82,722	103,198
Other operating expense	47,483	59,511	93,950	112,416
Net direct contribution	130,481	128,276	255,133	252,940
Gain (loss) on financial instruments, net	9	3	16	41
Change in fair value of mortgage servicing rights	0	0	0	0
Gain (loss) on repossessed assets, net	(67)	1,403	(4,232)	1,398
Corporate expense allocations	11,269	8,955	23,776	17,674
Net income before taxes	119,154	120,727	227,141	236,705
Federal and state income taxes	31,577	49,382	60,319	96,949
Net income	87,577	71,345	166,822	139,756
Net income attributable to non-controlling interests	0	0	0	0
Net income attributable to BOK Financial Corp. shareholders	87,577	71,345	166,822	139,756
Average assets	18,072,155	17,791,671	17,933,756	17,716,738
Operating Segments [Member] | Consumer [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	21,746	20,756	43,499	39,348
Net interest revenue (expense) from internal sources	17,548	13,447	32,772	25,864
Net interest revenue	39,294	34,203	76,271	65,212
Provision for credit losses	1,139	926	2,440	2,199
Net interest revenue after provision for credit losses	38,155	33,277	73,831	63,013
Other operating revenue	46,320	50,744	91,269	95,879
Other operating expense	55,906	55,125	105,760	107,991
Net direct contribution	28,569	28,896	59,340	50,901
Gain (loss) on financial instruments, net	(6,411)	5,224	(29,672)	3,557
Change in fair value of mortgage servicing rights	1,723	(6,943)	22,929	(5,087)
Gain (loss) on repossessed assets, net	174	98	66	(39)
Corporate expense allocations	15,867	16,912	31,897	33,658
Net income before taxes	8,188	10,363	20,766	15,674
Federal and state income taxes	2,086	4,031	5,288	6,097
Net income	6,102	6,332	15,478	9,577
Net income attributable to non-controlling interests	0	0	0	0
Net income attributable to BOK Financial Corp. shareholders	6,102	6,332	15,478	9,577
Average assets	8,353,558	8,441,831	8,410,513	8,360,022
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	18,754	10,475	34,161	21,960
Net interest revenue (expense) from internal sources	10,232	10,325	20,164	19,181
Net interest revenue	28,986	20,800	54,325	41,141
Provision for credit losses	(105)	(92)	(153)	(53)
Net interest revenue after provision for credit losses	29,091	20,892	54,478	41,194
Other operating revenue	70,642	75,569	145,409	149,727
Other operating expense	61,491	60,616	124,295	121,025
Net direct contribution	38,242	35,845	75,592	69,896
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	11,142	9,947	22,097	20,619
Net income before taxes	27,100	25,898	53,495	49,277
Federal and state income taxes	6,981	10,209	13,767	19,429
Net income	20,119	15,689	39,728	29,848
Net income attributable to non-controlling interests	0	0	0	0
Net income attributable to BOK Financial Corp. shareholders	20,119	15,689	39,728	29,848
Average assets	8,495,557	6,960,872	8,296,780	6,960,872
Funds Management and Other [Member]
Segment Reporting Information [Line Items]
Net interest revenue from external sources	15,935	19,596	38,097	43,325
Net interest revenue (expense) from internal sources	9,322	(2,057)	12,509	(5,214)
Net interest revenue	25,257	17,539	50,606	38,111
Provision for credit losses	(11,142)	(2,062)	(18,022)	(1,910)
Net interest revenue after provision for credit losses	36,399	19,601	68,628	40,021
Other operating revenue	(3,610)	(414)	(7,012)	3,744
Other operating expense	81,596	75,633	166,901	154,164
Net direct contribution	(48,807)	(56,446)	(105,285)	(110,399)
Gain (loss) on financial instruments, net	6,402	(5,227)	29,656	(3,598)
Change in fair value of mortgage servicing rights	(1,723)	6,943	(22,929)	5,087
Gain (loss) on repossessed assets, net	(107)	(1,501)	4,166	(1,359)
Corporate expense allocations	(38,278)	(35,814)	(77,770)	(71,951)
Net income before taxes	(5,957)	(20,417)	(16,622)	(38,318)
Federal and state income taxes	(7,314)	(15,917)	(15,096)	(36,667)
Net income	1,357	(4,500)	(1,526)	(1,651)
Net income attributable to non-controlling interests	783	719	568	1,027
Net income attributable to BOK Financial Corp. shareholders	574	(5,219)	(2,094)	(2,678)
Average assets	$ (1,015,235)	$ (825,803)	$ (825,055)	$ (377,472)