Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common stock, authorized (in shares)		2,500,000,000	2,500,000,000
Common stock, par value (in dollars per share)		$ 0.00006	$ 0.00006
Dividends declared and paid		$ 115,281	$ 111,026	$ 104,722
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		56,673	(25,623)	149,920
Net change in unrealized gain (loss)		(46,803)	136,775	(275,945)
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		(503)	(1,216)	(3,210)
Interest expense, Subordinated debentures		121	296	262
Net impairment losses recognized in earnings		1,819	373	2,308
Gain on available for sale securities, net		(12,058)	(1,539)	(10,720)
Other comprehensive income (loss), before income taxes		(57,424)	134,689	(287,305)
Federal and state income taxes	[1]	(22,338)	52,393	(111,762)
Other comprehensive income (loss), net of income taxes		(35,086)	82,296	(175,543)
Ending balance		$ 21,587	$ 56,673	(25,623)
Total Capital (to Risk Weighted Assets) [Abstract]
Total Capital Ratio Required to be Well Capitalized		10.00%	10.00%
Minimum Capital Requirement, Total Capital to Risk Weighted Assets	[2]	4.50%
Capital Conservation Buffer, Total Capital to Risk Weighted Assets	[3]	2.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Total Capital to Risk Weighted Assets		7.00%
Total Capital		$ 3,116,144	$ 3,120,223
Total Capital to Risk Weighted Assets		13.30%	14.66%
Common Equity Tier 1 (to Risk Weighted Assets) [Abstract]
Common Equity Tier 1 Capital Ratio Required to be Well Capitalized		6.50%
Minimum Capital Requirement, Common equity Tier 1 Capital to Risk Weighted Assets	[2]	6.00%
Capital Conservation Buffer, Common equity Tier 1 to Risk Weighted Assets	[3]	2.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Common equity Tier 1 to Risk Weighted Assets		8.50%
Common Equity Tier 1 Capital		$ 2,842,193
Common Equity Tier One Risk Based Capital to Risk Weighted Assets		12.13%
Tier I Capital (to Risk Weighted Assets) [Abstract]
Tier I Capital Ratio Required to be Well Capitalized		8.00%	6.00%
Minimum Capital Requirement, Tier 1 Capital to Risk Weighted Assets	[2]	8.00%
Capital Conservation Buffer, Tier 1 Capital to Risk Weighted Assets	[3]	2.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Tier One to Risk Weighted Assets		10.50%
Tier 1 Capital		$ 2,842,193	$ 2,838,129
Tier I Capital to Risk Weighted Assets		12.13%	13.33%
Tier I Capital (to Average Assets) [Abstract]
Leverage Ratio Required to be Well Capitalized		5.00%	5.00%
Minimum Capital Requirement, Tier 1 Capital to Average Assets	[2]	4.00%
Minimum Capital Requirements Including Capital Conservation Buffer, Tier One Capital to Average Assets		4.00%
Tier I Capital to Average Assets		9.25%	9.96%
Accumulated Unrealized Gain (Loss) on Available for Sale Securities [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		$ 59,239	$ (23,175)	155,553
Net change in unrealized gain (loss)		(48,607)	136,050	(284,104)
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		0	0	0
Interest expense, Subordinated debentures		0	0	0
Net impairment losses recognized in earnings		1,819	373	2,308
Gain on available for sale securities, net		(12,058)	(1,539)	(10,720)
Other comprehensive income (loss), before income taxes		(58,846)	134,884	(292,516)
Federal and state income taxes	[1]	(22,891)	52,470	(113,788)
Other comprehensive income (loss), net of income taxes		(35,955)	82,414	(178,728)
Ending balance		23,284	59,239	(23,175)
Accumulated Unrealized Gain on Investment Securities Transferred from AFS [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		376	1,118	3,078
Net change in unrealized gain (loss)		0	0	0
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		(503)	(1,216)	(3,210)
Interest expense, Subordinated debentures		0	0	0
Net impairment losses recognized in earnings		0	0	0
Gain on available for sale securities, net		0	0	0
Other comprehensive income (loss), before income taxes		(503)	(1,216)	(3,210)
Federal and state income taxes	[1]	(195)	(474)	(1,250)
Other comprehensive income (loss), net of income taxes		(308)	(742)	(1,960)
Ending balance		68	376	1,118
Accumulated Unrealized Gain (Loss) on Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		(2,868)	(3,311)	(8,296)
Net change in unrealized gain (loss)		1,804	725	8,159
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		0	0	0
Interest expense, Subordinated debentures		0	0	0
Net impairment losses recognized in earnings		0	0	0
Gain on available for sale securities, net		0	0	0
Other comprehensive income (loss), before income taxes		1,804	725	8,159
Federal and state income taxes	[1]	701	282	3,174
Other comprehensive income (loss), net of income taxes		1,103	443	4,985
Ending balance		(1,765)	(2,868)	(3,311)
Accumulated Loss on Effective Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance		(74)	(255)	(415)
Net change in unrealized gain (loss)		0	0	0
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities		0	0	0
Interest expense, Subordinated debentures		121	296	262
Net impairment losses recognized in earnings		0	0	0
Gain on available for sale securities, net		0	0	0
Other comprehensive income (loss), before income taxes		121	296	262
Federal and state income taxes	[1]	47	115	102
Other comprehensive income (loss), net of income taxes		74	181	160
Ending balance		0	(74)	(255)
BOKF, NA [Member]
Allowed dividends without regulatory approval		100,000
Dividends declared and paid		$ 150,000	75,000	$ 225,000
Maximum percentage of unimpaired capital on loan commitments and equity investments to a single affiliate (in hundredths)		10.00%
Maximum percentage of unimpaired capital on loan commitments and equity investments to all affiliates (in hundredths)		20.00%
Maximum loan commitments and equity investments to a single affiliate		$ 266,000
Maximum loan commitments and equity investments to all affiliates		532,000
Largest loan commitment and equity investment to a single affiliate		220,000
Aggregate loan commitment and equity investment to all affiliates		330,000	330,000
Largest amount outstanding to a single affiliate		218,000
Outstanding amounts to all affiliates		$ 244,000	18,000
Total Capital (to Risk Weighted Assets) [Abstract]
Minimum Capital Requirement, Total Capital to Risk Weighted Assets	[2]	4.50%
Minimum Capital Requirement Including Capital Conservation Buffer, Total Capital to Risk Weighted Assets		4.50%
Total Capital		$ 2,657,935	$ 2,449,078
Total Capital to Risk Weighted Assets		11.43%	11.56%
Common Equity Tier 1 (to Risk Weighted Assets) [Abstract]
Minimum Capital Requirement, Common equity Tier 1 Capital to Risk Weighted Assets	[2]	6.00%
Minimum Capital Requirement Including Capital Conservation Buffer, Common equity Tier 1 to Risk Weighted Assets		6.00%
Common Equity Tier 1 Capital		$ 2,385,323
Common Equity Tier One Risk Based Capital to Risk Weighted Assets		10.26%
Tier I Capital (to Risk Weighted Assets) [Abstract]
Minimum Capital Requirement, Tier 1 Capital to Risk Weighted Assets	[2]	8.00%
Minimum Capital Requirement Including Capital Conservation Buffer, Tier One to Risk Weighted Assets		8.00%
Tier 1 Capital		$ 2,385,323	$ 2,168,161
Tier I Capital to Risk Weighted Assets		10.26%	10.24%
Tier I Capital (to Average Assets) [Abstract]
Minimum Capital Requirement, Tier 1 Capital to Average Assets	[2]	4.00%
Minimum Capital Requirements Including Capital Conservation Buffer, Tier One Capital to Average Assets		4.00%
Tier I Capital to Average Assets		7.81%	7.65%
Perpetual stock [Member]
Preferred stock, authorized (in shares)		1,000,000,000
Preferred stock at par value (in dollars per share)		$ 0.00005
Preferred stock conversion rate		one share of Common Stock for each 36 shares of Series A Preferred Stock at the option of the holder
Preferred stock, Rate of annual cumulative dividends (in hundredths)		10.00%
Preferred stock, Liquidation preference per share		$ 0.06
Preferred stock, Aggregate liquidation preference		$ 15,000
Preferred Stock, Shares Outstanding		0	0	0
Common Stock [Member]
Common stock, authorized (in shares)		2,500,000,000
Common stock, par value (in dollars per share)		$ 0.00006
Common stock, number of vote per share		$ 1

[1] Calculated using 39% effective tax rate.

[2] Effective January 1, 2015

[3] Effective January 1, 2016