Loans and Allowances for Credit Losses, Activity in Allowance for Credit Losses (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowance for loan losses [Roll Forward]
Beginning balance	$ 185,396,000	$ 215,507,000	$ 253,481,000
Provision for loan losses	858,000	(28,073,000)	(14,654,000)
Loans charged off	(16,232,000)	(25,282,000)	(42,138,000)
Recoveries	19,034,000	23,244,000	18,818,000
Ending balance	189,056,000	185,396,000	215,507,000
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	2,088,000	1,915,000	9,261,000
Provision for off-balance sheet credit risk	(858,000)	173,000	(7,346,000)
Ending balance	1,230,000	2,088,000	1,915,000
Total provision for credit losses	0	(27,900,000)	(22,000,000)
Negative recovery related to invalidated settlement agreement			7,100,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	14,127,266,000	12,691,892,000
Individually measured for impairment, recorded investment	80,771,000	100,372,000
Total	14,208,037,000	12,792,264,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance	160,699,000	156,229,000
Individually measured for impairment, related allowance	312,000	954,000
Total measured for impairment, related allowance	189,056,000	185,396,000	215,507,000
Commercial [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	79,180,000	65,280,000	83,443,000
Provision for loan losses	9,561,000	12,747,000	(14,950,000)
Loans charged off	(3,569,000)	(6,335,000)	(9,341,000)
Recoveries	5,703,000	7,488,000	6,128,000	[1]
Ending balance	90,875,000	79,180,000	65,280,000
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	119,000	475,000	7,906,000
Provision for off-balance sheet credit risk	356,000	(356,000)	(7,431,000)
Ending balance	475,000	119,000	475,000
Total provision for credit losses	9,917,000	12,391,000	(22,381,000)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	9,082,143,000	7,926,461,000
Individually measured for impairment, recorded investment	13,527,000	16,760,000
Total	9,095,670,000	7,943,221,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance	90,709,000	78,607,000
Individually measured for impairment, related allowance	166,000	573,000
Total measured for impairment, related allowance	90,875,000	79,180,000	65,280,000
Commercial Real Estate [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	41,573,000	54,884,000	67,034,000
Provision for loan losses	(4,084,000)	(16,886,000)	(6,214,000)
Loans charged off	(2,047,000)	(5,845,000)	(11,642,000)
Recoveries	7,003,000	9,420,000	5,706,000
Ending balance	42,445,000	41,573,000	54,884,000
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	1,876,000	1,353,000	1,250,000
Provision for off-balance sheet credit risk	(1,169,000)	523,000	103,000
Ending balance	707,000	1,876,000	1,353,000
Total provision for credit losses	(5,253,000)	(16,363,000)	(6,111,000)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	2,709,593,000	2,374,503,000
Individually measured for impairment, recorded investment	18,557,000	40,850,000
Total	2,728,150,000	2,415,353,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance	42,404,000	41,440,000
Individually measured for impairment, related allowance	41,000	133,000
Total measured for impairment, related allowance	42,445,000	41,573,000	54,884,000
Residential Mortgage [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	29,465,000	41,703,000	46,476,000
Provision for loan losses	(3,559,000)	(8,043,000)	3,346,000
Loans charged off	(4,448,000)	(5,753,000)	(10,047,000)
Recoveries	2,000,000	1,558,000	1,928,000
Ending balance	23,458,000	29,465,000	41,703,000
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	90,000	78,000	91,000
Provision for off-balance sheet credit risk	(62,000)	12,000	(13,000)
Ending balance	28,000	90,000	78,000
Total provision for credit losses	(3,621,000)	(8,031,000)	3,333,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	1,901,391,000	2,010,483,000
Individually measured for impairment, recorded investment	48,121,000	41,543,000
Total	1,949,512,000	2,052,026,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance	23,353,000	29,217,000
Individually measured for impairment, related allowance	105,000	248,000
Total measured for impairment, related allowance	23,458,000	29,465,000	41,703,000
Consumer [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	6,965,000	9,453,000	10,178,000
Provision for loan losses	(892,000)	83,000	5,327,000
Loans charged off	(6,168,000)	(7,349,000)	(11,108,000)
Recoveries	4,328,000	4,778,000	5,056,000
Ending balance	4,233,000	6,965,000	9,453,000
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	3,000	9,000	14,000
Provision for off-balance sheet credit risk	17,000	(6,000)	(5,000)
Ending balance	20,000	3,000	9,000
Total provision for credit losses	(875,000)	77,000	5,322,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	434,139,000	380,445,000
Individually measured for impairment, recorded investment	566,000	1,219,000
Total	434,705,000	381,664,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance	4,233,000	6,965,000
Individually measured for impairment, related allowance	0	0
Total measured for impairment, related allowance	4,233,000	6,965,000	9,453,000
Specific Allowance [Member]
Allowance for loan losses [Roll Forward]
Ending balance	161,011,000	157,183,000
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	14,127,266,000	12,691,892,000
Individually measured for impairment, recorded investment	80,771,000	100,372,000
Total	14,208,037,000	12,792,264,000
Related allowance [Abstract]
Collectively measured for impairment, related allowance	160,699,000	156,229,000
Individually measured for impairment, related allowance	312,000	954,000
Total measured for impairment, related allowance	161,011,000	157,183,000
Nonspecific allowance [Member]
Allowance for loan losses [Roll Forward]
Beginning balance	28,213,000	44,187,000	46,350,000
Provision for loan losses	(168,000)	(15,974,000)	(2,163,000)
Loans charged off	0	0	0
Recoveries	0	0	0
Ending balance	28,045,000	28,213,000	44,187,000
Accrual for off-balance sheet credit losses [Roll Forward]
Beginning balance	0	0	0
Provision for off-balance sheet credit risk	0	0	0
Ending balance	0	0	0
Total provision for credit losses	(168,000)	(15,974,000)	(2,163,000)
Recorded investment [Abstract]
Collectively measured for impairment, recorded investment	0	0
Individually measured for impairment, recorded investment	0	0
Total	0	0
Related allowance [Abstract]
Collectively measured for impairment, related allowance	0	0
Individually measured for impairment, related allowance	0	0
Total measured for impairment, related allowance	$ 28,045,000	$ 28,213,000	$ 44,187,000

[1] Includes $7.1 million of negative recovery related to a refund of a settlement between BOK Financial and the City of Tulsa invalidated by the Oklahoma Supreme Court.