Reportable Segments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Tax-equivalent net interest revenue from external sources	$ 219,736	$ 201,182
Tax-equivalent net interest revenue (expense) from internal sources	0	0
Net interest revenue	219,736	201,182
Provision for credit losses	(5,000)	0
Net interest revenue after provision for credit losses	224,736	201,182
Other operating revenue	155,989	170,296
Other operating expense	244,430	244,711
Net direct contribution	136,295	126,767
Gain (loss) on financial instruments, net	0	0
Change in fair value of mortgage servicing rights	0	0
Loss on repossessed assets, net	0	0
Corporate expense allocations	0	0
Net income before taxes	136,295	126,767
Federal and state income taxes	30,948	38,103
Net income	105,347	88,664
Net income (loss) attributable to non-controlling interests	(215)	308
Net income attributable to BOK Financial Corp. shareholders	105,562	88,356
Average assets	33,724,952	32,954,989
Operating Segments [Member] | Commercial [Member]
Segment Reporting Information [Line Items]
Tax-equivalent net interest revenue from external sources	160,413	147,376
Tax-equivalent net interest revenue (expense) from internal sources	(28,343)	(18,115)
Net interest revenue	132,070	129,261
Provision for credit losses	627	(1,463)
Net interest revenue after provision for credit losses	131,443	130,724
Other operating revenue	39,676	46,844
Other operating expense	46,469	52,905
Net direct contribution	124,650	124,663
Gain (loss) on financial instruments, net	7	38
Change in fair value of mortgage servicing rights	0	0
Loss on repossessed assets, net	(4,166)	(5)
Corporate expense allocations	12,507	8,719
Net income before taxes	107,984	115,977
Federal and state income taxes	28,741	47,568
Net income	79,243	68,409
Net income (loss) attributable to non-controlling interests	0	0
Net income attributable to BOK Financial Corp. shareholders	79,243	68,409
Average assets	17,793,820	17,640,973
Operating Segments [Member] | Consumer [Member]
Segment Reporting Information [Line Items]
Tax-equivalent net interest revenue from external sources	21,755	18,593
Tax-equivalent net interest revenue (expense) from internal sources	15,224	12,418
Net interest revenue	36,979	31,011
Provision for credit losses	1,301	1,273
Net interest revenue after provision for credit losses	35,678	29,738
Other operating revenue	44,948	45,134
Other operating expense	49,813	52,866
Net direct contribution	30,813	22,006
Gain (loss) on financial instruments, net	(23,262)	(1,668)
Change in fair value of mortgage servicing rights	21,206	1,856
Loss on repossessed assets, net	(108)	(136)
Corporate expense allocations	16,029	16,746
Net income before taxes	12,620	5,312
Federal and state income taxes	3,214	2,066
Net income	9,406	3,246
Net income (loss) attributable to non-controlling interests	0	0
Net income attributable to BOK Financial Corp. shareholders	9,406	3,246
Average assets	8,468,101	8,277,304
Operating Segments [Member] | Wealth Management [Member]
Segment Reporting Information [Line Items]
Tax-equivalent net interest revenue from external sources	15,407	11,485
Tax-equivalent net interest revenue (expense) from internal sources	9,932	8,856
Net interest revenue	25,339	20,341
Provision for credit losses	(48)	39
Net interest revenue after provision for credit losses	25,387	20,302
Other operating revenue	74,766	74,158
Other operating expense	62,802	60,410
Net direct contribution	37,351	34,050
Gain (loss) on financial instruments, net	0	0
Change in fair value of mortgage servicing rights	0	0
Loss on repossessed assets, net	0	0
Corporate expense allocations	10,955	10,672
Net income before taxes	26,396	23,378
Federal and state income taxes	6,787	9,219
Net income	19,609	14,159
Net income (loss) attributable to non-controlling interests	0	0
Net income attributable to BOK Financial Corp. shareholders	19,609	14,159
Average assets	8,095,794	7,160,849
Funds Management and Other [Member]
Segment Reporting Information [Line Items]
Tax-equivalent net interest revenue from external sources	22,161	23,728
Tax-equivalent net interest revenue (expense) from internal sources	3,187	(3,159)
Net interest revenue	25,348	20,569
Provision for credit losses	(6,880)	151
Net interest revenue after provision for credit losses	32,228	20,418
Other operating revenue	(3,401)	4,160
Other operating expense	85,346	78,530
Net direct contribution	(56,519)	(53,952)
Gain (loss) on financial instruments, net	23,255	1,630
Change in fair value of mortgage servicing rights	(21,206)	(1,856)
Loss on repossessed assets, net	4,274	141
Corporate expense allocations	(39,491)	(36,137)
Net income before taxes	(10,705)	(17,900)
Federal and state income taxes	(7,794)	(20,750)
Net income	(2,911)	2,850
Net income (loss) attributable to non-controlling interests	(215)	308
Net income attributable to BOK Financial Corp. shareholders	(2,696)	2,542
Average assets	$ (632,763)	$ (124,137)