Consolidated Statements of Earnings - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest and dividend revenue [Abstract]
Loans	$ 696,479	$ 581,030	$ 529,683
Residential mortgage loans held for sale	8,706	12,658	13,602
Trading securities	17,002	8,527	2,240
Investment securities	16,121	16,894	18,098
Available for sale securities	177,070	175,321	174,829
Fair value option securities	16,755	6,723	9,264
Restricted equity securities	18,490	17,238	13,532
Interest-bearing cash and cash equivalents	22,128	10,726	5,580
Total interest and dividend revenue	972,751	829,117	766,828
Interest expense [Abstract]
Deposits	53,803	40,494	44,170
Borrowed funds	69,124	35,336	14,204
Subordinated debentures	8,123	6,059	5,100
Total interest expense	131,050	81,889	63,474
Net interest and dividend revenue	841,701	747,228	703,354
Provision for credit losses	(7,000)	65,000	34,000
Net interest and dividend revenue after provision for credit losses	848,701	682,228	669,354
Other operating revenue [Abstract]
Brokerage and trading revenue	131,601	138,377	129,556
Transaction card revenue	119,988	116,452	109,579
Fiduciary and asset management revenue	162,893	135,477	126,153
Deposit service charges and fees	112,075	111,499	109,473
Mortgage banking revenue	104,719	133,914	126,002
Other revenue	52,168	51,029	49,883
Total fees and commissions	683,444	686,748	650,646
Other gains, net	9,004	4,030	5,702
Gain (loss) on derivatives, net	779	(15,685)	430
Loss on fair value option securities, net	(2,733)	(10,555)	(3,684)
Change in fair value of mortgage servicing rights	172	(2,193)	(4,853)
Gain on available for sale securities, net	4,428	11,675	12,058
Total other-than-temporary impairment losses	0	0	(2,443)
Portion of loss recognized in other comprehensive income	0	0	624
Net impairment losses recognized in earnings	0	0	(1,819)
Total other operating revenue	695,094	674,020	658,480
Other operating expense [Abstract]
Personnel	573,408	553,119	515,298
Business promotion	28,877	26,582	27,851
Charitable contributions to BOKF Foundation	2,000	2,000	796
Professional fees and services	51,067	56,783	40,123
Net occupancy and equipment	86,477	80,024	76,016
Insurance	19,653	32,489	20,375
Data processing and communications	146,970	131,841	122,383
Printing, postage and supplies	15,689	15,584	13,498
Net losses and operating expenses of repossessed assets	9,687	3,359	1,446
Amortization of intangible assets	6,779	6,862	4,359
Mortgage banking costs	52,856	61,387	38,813
Other expense	32,054	47,560	35,233
Total other operating expense	1,025,517	1,017,590	896,191
Net income before taxes	518,278	338,658	431,643
Federal and state income taxes	182,593	106,377	139,384
Net income	335,685	232,281	292,259
Net income (loss) attributable to Non-controlling interests	1,041	(387)	3,694
Net income attributable to BOK Financial Corporation shareholders	$ 334,644	$ 232,668	$ 288,565
Earnings per share: [Abstract]
Basic (in dollars per share)	$ 5.11	$ 3.53	$ 4.22
Diluted (in dollars per share)	$ 5.11	$ 3.53	$ 4.21
Average shares used in computation: [Abstract]
Basic (in shares)	64,745,364	65,085,627	67,594,689
Diluted (in shares)	64,806,284	65,143,898	67,691,658
Dividends declared per share (in dollars per share)	$ 1.77	$ 1.73	$ 1.69