Shareholders' Equity (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Jan. 01, 2015
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	$ 111,026,000		$ 104,722,000		$ 166,982,000
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(25,623,000)		149,920,000		128,979,000
Net change in unrealized gain (loss)	136,775,000		(275,945,000)		66,197,000
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities	(1,216,000)		(3,210,000)		(6,601,000)
Interest expense, Subordinated debentures	296,000		262,000		453,000
Net impairment losses recognized in earnings	373,000		2,308,000		7,351,000
Gain on available for sale securities, net	(1,539,000)		(10,720,000)		(33,845,000)
Other comprehensive income (loss), before income taxes	134,689,000		(287,305,000)		33,555,000
Federal and state income taxes	(52,393,000)	[1]	111,762,000	[1]	(12,614,000)	[1]
Other comprehensive income (loss), net of income taxes	82,296,000		(175,543,000)		20,941,000
Ending balance	56,673,000		(25,623,000)		149,920,000
Total Capital (to Risk Weighted Assets) [Abstract]
Total Capital Ratio Required to be Well Capitalized	10.00%		10.00%
Total Capital	3,120,223,000		3,017,022,000
Total Capital to Risk Weighted Assets	14.66%		15.56%
Tier I Capital (to Risk Weighted Assets) [Abstract]
Tier I Capital Ratio Required to be Well Capitalized	6.00%		6.00%
Tier I Capital	2,838,129,000		2,668,981,000
Tier I Capital to Risk Weighted Assets	13.33%		13.77%
Tier I Capital (to Average Assets) [Abstract]
Leverage Ratio Required to be Well Capitalized	5.00%		5.00%
Tier I Capital to Average Assets	9.96%		10.05%
Accumulated Net Unrealized Gain (Loss) on Available for Sale Securities [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(23,175,000)		155,553,000		135,740,000
Net change in unrealized gain (loss)	136,050,000		(284,104,000)		58,921,000
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	373,000		2,308,000		7,351,000
Gain on available for sale securities, net	(1,539,000)		(10,720,000)		(33,845,000)
Other comprehensive income (loss), before income taxes	134,884,000		(292,516,000)		32,427,000
Federal and state income taxes	(52,470,000)	[1]	113,788,000	[1]	(12,614,000)	[1]
Other comprehensive income (loss), net of income taxes	82,414,000		(178,728,000)		19,813,000
Ending balance	59,239,000		(23,175,000)		155,553,000
Accumulated Unrealized Gain on Investment Securities Transferred from AFS [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	1,118,000		3,078,000		6,673,000
Net change in unrealized gain (loss)	0		0		0
Reclassification adjustments included in earnings: [Abstract]
Interest revenue, Investment securities, Taxable securities	(1,216,000)		(3,210,000)		(6,601,000)
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	(1,216,000)		(3,210,000)		(6,601,000)
Federal and state income taxes	474,000	[1]	1,250,000	[1]	3,006,000	[1]
Other comprehensive income (loss), net of income taxes	(742,000)		(1,960,000)		(3,595,000)
Ending balance	376,000		1,118,000		3,078,000
Accumulated Unrealized Gain (Loss) on Employee Benefit Plans [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(3,311,000)		(8,296,000)		(12,742,000)
Net change in unrealized gain (loss)	725,000		8,159,000		7,276,000
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	725,000		8,159,000		7,276,000
Federal and state income taxes	(282,000)	[1]	(3,174,000)	[1]	(2,830,000)	[1]
Other comprehensive income (loss), net of income taxes	443,000		4,985,000		4,446,000
Ending balance	(2,868,000)		(3,311,000)		(8,296,000)
Accumulated Loss on Effective Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	(255,000)		(415,000)		(692,000)
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	296,000		262,000		453,000
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	296,000		262,000		453,000
Federal and state income taxes	(115,000)	[1]	(102,000)	[1]	(176,000)	[1]
Other comprehensive income (loss), net of income taxes	181,000		160,000		277,000
Ending balance	(74,000)		(255,000)		(415,000)
BOKF, NA [Member]
Allowed dividends without regulatory approval	365,000,000
Available dividend capacity of subsidiary bank upon implementation of Basel III Capital Rules							0
Dividends declared and paid	75,000,000		225,000,000		275,000,000
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	245,000,000
Maximum loan commitments and equity investments to all affiliates	490,000,000
Largest loan commitment and equity investment to a single affiliate	220,000,000
Aggregate loan commitment and equity investment to all affiliates	330,000,000		334,000,000
Largest amount outstanding to a single affiliate	14,000,000
Outstanding amounts to all affiliates	18,000,000		27,000,000
Total Capital (to Risk Weighted Assets) [Abstract]
Total Capital	2,449,078,000		2,293,673,000
Total Capital to Risk Weighted Assets	11.56%		11.88%
Tier I Capital (to Risk Weighted Assets) [Abstract]
Tier I Capital	2,168,161,000		1,946,247,000
Tier I Capital to Risk Weighted Assets	10.24%		10.08%
Tier I Capital (to Average Assets) [Abstract]
Tier I Capital to Average Assets	7.65%		7.38%
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	$ 15,000,000
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] 1 Calculated using 39% effective tax rate.