Consolidated Statements of Earnings (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Interest revenue [Abstract]
Loans	$ 218,732	$ 184,200	$ 617,517	$ 514,047
Residential mortgage loans held for sale	2,151	2,095	6,328	6,317
Trading securities	17,295	3,975	38,021	12,497
Investment securities	3,598	3,951	11,118	12,127
Available for sale securities	48,917	44,925	142,303	131,660
Fair value option securities	3,881	5,066	12,627	10,985
Restricted equity securities	5,232	4,826	15,757	13,534
Interest-bearing cash and cash equivalents	3,441	6,375	19,163	15,817
Total interest revenue	303,247	255,413	862,834	716,984
Interest expense [Abstract]
Deposits	24,535	14,530	63,717	38,506
Borrowed funds	35,804	20,361	93,860	47,542
Subordinated debentures	2,025	2,070	6,076	6,098
Total interest expense	62,364	36,961	163,653	92,146
Net interest revenue	240,883	218,452	699,181	624,838
Provision for credit losses	4,000	0	(1,000)	0
Net interest revenue after provision for credit losses	236,883	218,452	700,181	624,838
Total fees and commissions	167,510	173,451	484,349	515,287
Other gains, net	1,441	(1,283)	4,760	8,452
Gain (loss) on derivatives, net	(2,847)	1,033	(11,589)	3,824
Gain (loss) on fair value option securities, net	(4,385)	661	(25,290)	1,505
Change in fair value of mortgage servicing rights	5,972	(639)	28,901	(5,726)
Gain (loss) on available for sale securities, net	250	2,487	(802)	4,916
Total other operating revenue	167,941	175,710	480,329	528,258
Other operating expense [Abstract]
Personnel	143,531	147,910	422,425	428,079
Business promotion	7,620	7,105	21,316	21,560
Professional fees and services	13,209	11,887	38,387	35,723
Net occupancy and equipment	23,394	21,325	70,201	64,074
Insurance	6,232	6,005	19,070	13,098
Data processing and communications	31,665	37,327	87,221	108,559
Printing, postage and supplies	3,837	3,917	11,937	11,908
Net losses and operating expenses of repossessed assets	4,044	6,071	14,471	9,347
Amortization of intangible assets	1,603	1,744	4,289	5,349
Mortgage banking costs	11,741	13,450	34,780	38,525
Other expense	5,741	9,193	19,426	25,308
Total other operating expense	252,617	265,934	743,523	761,530
Net income before taxes	152,207	128,228	436,987	391,566
Federal and state income taxes	34,662	42,438	98,940	128,246
Net income	117,545	85,790	338,047	263,320
Net income attributable to non-controlling interests	289	141	857	1,168
Net income attributable to BOK Financial Corporation shareholders	$ 117,256	$ 85,649	$ 337,190	$ 262,152
Earnings per share: [Abstract]
Basic	$ 1.79	$ 1.31	$ 5.15	$ 4.01
Diluted	$ 1.79	$ 1.31	$ 5.15	$ 4.00
Average shares used in computation: [Abstract]
Basic	64,901,095	64,742,822	64,883,319	64,729,391
Diluted	64,934,351	64,805,172	64,919,728	64,793,893
Dividends declared per share	$ 0.50	$ 0.44	$ 1.40	$ 1.32
Brokerage and trading revenue [Member]
Total fees and commissions	$ 23,086	$ 33,169	$ 80,222	$ 98,556
Transaction card revenue [Member]
Total fees and commissions	21,396	32,844	63,361	90,452
Fiduciary and asset management revenue [Member]
Total fees and commissions	57,514	40,687	141,045	121,126
Deposit service charges and fees [Member]
Total fees and commissions	27,765	28,191	82,753	84,390
Mortgage banking revenue [Member]
Total fees and commissions	23,536	24,890	75,907	80,357
Other revenue [Member]
Total fees and commissions	$ 14,213	$ 13,670	$ 41,061	$ 40,406