Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Cash Flows From Operating Activities: [Abstract]
Net income	$ 231,183	$ 229,898
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Provision for credit losses	11,500	0
Change in fair value of mortgage servicing rights	12,269	5,624
Unrealized gains from derivative contracts	(974)	(7,853)
Tax effect from equity compensation, net	(645)	(8,176)
Change in bank-owned life insurance	(6,956)	(6,706)
Share-based compensation	7,807	11,815
Depreciation and amortization	50,088	40,833
Net amortization of securities discounts and premiums	42,757	43,078
Net realized losses (gains) on financial instruments and other assets	(12,601)	1,459
Net gain on mortgage loans held for sale	(60,075)	(43,764)
Mortgage loans originated for sale	(5,007,471)	(3,220,120)
Proceeds from sale of mortgage loans held for sale	5,022,109	3,091,285
Capitalized mortgage servicing rights	(62,375)	(39,183)
Charitable contributions to BOKF Foundation	796	2,420
Change in trading and fair value option securities	(110,857)	(88,005)
Change in receivables	8,455	14,134
Change in other assets	(8,412)	36,931
Change in accrued interest, taxes and expense	14,447	(107,585)
Change in other liabilities	40,670	23,164
Net cash provided by (used in) operating activities	171,715	(20,751)
Cash Flows From Investing Activities: [Abstract]
Proceeds from maturities or redemptions of investment securities	53,795	54,666
Proceeds from maturities or redemptions of available for sale securities	1,307,177	1,323,708
Purchases of investment securities	(19,037)	(37,094)
Purchases of available for sale securities	(2,271,374)	(2,324,730)
Proceeds from sales of available for sale securities	1,164,425	1,884,061
Change in amount receivable on unsettled securities transactions	44,250	(77,707)
Loans originated, net of principal collected	(1,121,100)	(845,432)
Net payments on derivative asset contracts	(291,949)	(102,302)
Acquisitions, net of cash acquired	(18,098)	(21,898)
Proceeds from disposition of assets	131,824	95,611
Purchases of assets	(203,546)	(193,597)
Net cash used in investing activities	(1,223,633)	(244,714)
Cash Flows From Financing Activities: [Abstract]
Net change in demand deposits, transaction deposits and savings accounts	(411,231)	51,142
Net change in time deposits	(110,185)	(31,413)
Net change in other borrowed funds	1,786,438	1,773,313
Repayment of subordinated debentures	(121,810)	0
Net proceeds on derivative liability contracts	277,872	114,985
Net change in derivative margin accounts	(148,119)	(45,724)
Change in amount due on unsettled security transactions	(192,189)	(37,614)
Issuance of common and treasury stock, net	4,797	(6,847)
Tax effect from equity compensation, net	645	8,176
Sale of non-controlling interests	5,500	0
Repurchase of common stock	(109,760)	0
Dividends paid	(86,509)	(82,207)
Net cash provided by financing activities	895,449	1,743,811
Net increase (decrease) in cash and cash equivalents	(156,469)	1,478,346
Cash and cash equivalents at beginning of period	2,475,842	1,087,213
Cash and cash equivalents at end of period	2,319,373	2,565,559
Supplemental Cash Flow Information: [Abstract]
Cash paid for interest	50,066	47,264
Cash paid for taxes	78,115	61,627
Net loans and bank premises transferred to repossessed real estate and other assets	9,558	38,797
Residential mortgage loans guaranteed by U.S. government agencies that became eligible for repurchase during the period	86,242	100,430
Conveyance of other real estate owned guaranteed by U.S. government agencies	93,157	34,425
Issuance of shares in settlement of accrued executive compensation	$ 0	$ 15,072