Consolidated Statements of Earnings - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest and dividend revenue [Abstract]
Loans	$ 891,587	$ 696,479	$ 581,030
Residential mortgage loans held for sale	8,123	8,706	12,658
Trading securities	57,531	17,002	8,527
Investment securities	14,775	16,121	16,894
Available for sale securities	197,317	177,070	175,321
Fair value option securities	15,205	16,755	6,723
Restricted equity securities	21,555	18,490	17,238
Interest-bearing cash and cash equivalents	22,333	22,128	10,726
Total interest revenue	1,228,426	972,751	829,117
Interest Expense [Abstract]
Deposits	95,517	53,803	40,494
Borrowed funds	138,215	69,124	35,099
Subordinated debentures	9,827	8,123	6,296
Total interest expense	243,559	131,050	81,889
Net interest and dividend revenue	984,867	841,701	747,228
Provision for credit losses	8,000	(7,000)	65,000
Net interest and dividend revenue after provision for credit losses	976,867	848,701	682,228
Total fees and commissions	643,642	681,235	685,831
Other gains (losses), net	(2,731)	11,213	4,947
Gain (loss) on derivatives, net	(422)	779	(15,685)
Loss on fair value option securities, net	(25,572)	(2,733)	(10,555)
Change in fair value of mortgage servicing rights	4,668	172	(2,193)
Gain (loss) on available for sale securities, net	(2,801)	4,428	11,675
Total other operating revenue	616,784	695,094	674,020
Other operating expense [Abstract]
Personnel	583,131	573,408	553,119
Business promotion	30,523	28,877	26,582
Charitable contributions to BOKF Foundation	2,846	2,000	2,000
Professional fees and services	59,099	51,067	56,783
Net occupancy and equipment	97,981	86,477	80,024
Insurance	23,318	19,653	32,489
Data processing and communications	114,796	146,970	131,841
Printing, postage and supplies	17,169	15,689	15,584
Net losses and operating expenses of repossessed assets	17,052	9,687	3,359
Amortization of intangible assets	9,620	6,779	6,862
Mortgage banking costs	46,298	52,856	61,387
Other expense	26,333	32,054	47,560
Total other operating expense	1,028,166	1,025,517	1,017,590
Net income before taxes	565,485	518,278	338,658
Federal and state income taxes	119,061	182,593	106,377
Net income	446,424	335,685	232,281
Net income (loss) attributable to Non-controlling interests	778	1,041	(387)
Net income attributable to BOK Financial Corporation shareholders	$ 445,646	$ 334,644	$ 232,668
Earnings per share: [Abstract]
Basic (in dollars per share)	$ 6.63	$ 5.11	$ 3.53
Diluted (in dollars per share)	$ 6.63	$ 5.11	$ 3.53
Average shares used in computation: [Abstract]
Basic (in shares)	66,628,640	64,745,364	65,085,627
Diluted (in shares)	66,662,273	64,806,284	65,143,898
Dividends declared per share (in dollars per share)	$ 1.90	$ 1.77	$ 1.73
Brokerage and trading revenue [Member]
Total fees and commissions	$ 108,323	$ 131,601	$ 138,377
Transaction card revenue [Member]
Total fees and commissions	84,025	119,988	116,452
Fiduciary and asset management revenue [Member]
Total fees and commissions	184,703	162,889	135,387
Deposit service charges and fees [Member]
Total fees and commissions	112,153	112,079	111,589
Mortgage banking revenue [Member]
Total fees and commissions	97,787	104,719	133,914
Other revenue [Member]
Total fees and commissions	$ 56,651	$ 49,959	$ 50,112