Consolidated Statements of Earnings (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Interest revenue [Abstract]
Loans	$ 210,694	$ 168,952	$ 398,785	$ 329,847
Residential mortgage loans held for sale	2,333	2,386	4,177	4,222
Trading securities	12,988	3,339	20,726	8,522
Investment securities	3,663	4,005	7,520	8,176
Available for sale securities	47,427	43,363	93,386	86,735
Fair value option securities	3,927	3,539	8,746	5,919
Restricted equity securities	5,408	4,399	10,525	8,708
Interest-bearing cash and cash equivalents	7,740	5,198	15,722	9,442
Total interest revenue	294,180	235,181	559,587	461,571
Interest expense [Abstract]
Deposits	20,963	12,622	39,182	23,976
Borrowed funds	32,607	15,352	58,056	27,181
Subordinated debentures	2,048	2,003	4,051	4,028
Total interest expense	55,618	29,977	101,289	55,185
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 [Abstract]
Brokerage and trading revenue	26,488	31,764	57,136	65,387
Transaction card revenue	20,975	30,228	41,965	57,608
Fiduciary and asset management revenue	41,699	41,808	83,531	80,439
Deposit service charges and fees	27,827	28,422	54,988	56,199
Mortgage banking revenue	26,346	30,276	52,371	55,467
Other revenue	14,518	14,984	26,848	26,736
Total fees and commissions	157,853	177,482	316,839	341,836
Other gains, net	3,983	6,108	3,319	9,735
Gain (loss) on derivatives, net	(3,057)	3,241	(8,742)	2,791
Gain (loss) on fair value option securities, net	(3,341)	1,984	(20,905)	844
Change in fair value of mortgage servicing rights	1,723	(6,943)	22,929	(5,087)
Gain (loss) on available for sale securities, net	(762)	380	(1,052)	2,429
Total other operating revenue	156,399	182,252	312,388	352,548
Other operating expense [Abstract]
Personnel	138,947	143,744	278,894	280,169
Business promotion	7,686	7,738	13,696	14,455
Professional fees and services	14,978	12,419	25,178	23,836
Net occupancy and equipment	22,761	21,125	46,807	42,749
Insurance	6,245	689	12,838	7,093
Data processing and communications	27,739	36,330	55,556	71,232
Printing, postage and supplies	4,011	4,140	8,100	7,991
Net losses and operating expenses of repossessed assets	2,722	2,267	10,427	3,276
Amortization of intangible assets	1,386	1,803	2,686	3,605
Mortgage banking costs	12,890	12,072	23,039	25,075
Other expense	7,111	8,558	13,685	16,115
Total other operating expense	246,476	250,885	490,906	495,596
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 Corporation shareholders	$ 114,372	$ 88,147	$ 219,934	$ 176,503
Earnings per share: [Abstract]
Basic	$ 1.75	$ 1.35	$ 3.36	$ 2.70
Diluted	$ 1.75	$ 1.35	$ 3.36	$ 2.69
Average shares used in computation: [Abstract]
Basic	64,901,975	64,729,752	64,874,567	64,722,744
Diluted	64,937,226	64,793,134	64,912,552	64,788,322
Dividends declared per share	$ 0.45	$ 0.44	$ 0.90	$ 0.88