Deposits (Details) (USD $)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Interest expense on deposits [Abstract]
Transaction deposits	$ 9,757,000	$ 11,155,000	$ 14,300,000
Savings	401,000us-gaap_InterestExpenseSavingsDeposits	442,000us-gaap_InterestExpenseSavingsDeposits	540,000us-gaap_InterestExpenseSavingsDeposits
Time Deposit, Interest Expense [Abstract]
Certificates of deposits under $100,000	14,278,000	16,234,000	19,150,000
Certificates of deposits $100,000 and over	11,878,000	12,273,000	16,331,000
Other time deposits	14,369,000bokf_InterestExpenseOnOtherTimeDeposits	15,460,000bokf_InterestExpenseOnOtherTimeDeposits	16,692,000bokf_InterestExpenseOnOtherTimeDeposits
Total time	40,525,000us-gaap_InterestExpenseTimeDeposits	43,967,000us-gaap_InterestExpenseTimeDeposits	52,173,000us-gaap_InterestExpenseTimeDeposits
Total	50,683,000us-gaap_InterestExpenseDeposits	55,564,000us-gaap_InterestExpenseDeposits	67,013,000us-gaap_InterestExpenseDeposits
Time Deposits [Abstract]
Time Deposits, $250,000 or More, Domestic	994,000,000bokf_TimeDeposits250000orMoreDomestic	988,000,000bokf_TimeDeposits250000orMoreDomestic
Time Deposit Maturities [Abstract]
2015	1,300,000,000us-gaap_TimeDepositMaturitiesYearOne
2016	519,000,000us-gaap_TimeDepositMaturitiesYearTwo
2017	170,000,000us-gaap_TimeDepositMaturitiesYearThree
2018	201,000,000us-gaap_TimeDepositMaturitiesYearFour
2019	81,000,000us-gaap_TimeDepositMaturitiesYearFive
Thereafter	290,000,000
Fixed rate, brokered certificates of deposits	334,000,000	186,000,000
Weighted-average interest rate paid on fixed rate, brokered certificates of deposits (in hundredths)	2.59%	2.96%
Other Deposits Information [Abstract]
Overdrawn transaction deposits reclassified as loan balances	$ 6,200,000	$ 37,000,000

Interest expense incurred on time deposits, other than certificates of deposits.

No definition available.

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The aggregate amount of domestic time deposits (including certificates of deposits, individual retirement accounts and open accounts) in denominations of $250,000 or more.

+ References

No definition available.

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- Definition

Amount of deposits held by the entity that have been reclassified as loan balances receivable, for example, but not limited to, overdrafts receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 405

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6479006&loc=d3e64164-112818

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- Definition

Amount of interest-bearing domestic third-party deposits placed by or through the assistance of a deposit broker, also known as brokered deposit liabilities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.12)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 12

-Article 9

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- Definition

Aggregate amount of interest expense on all deposits.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.6)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 6

-Article 9

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Interest expense incurred on the amount of Negotiable Order of Withdrawal (NOW). Interest-bearing transaction account that combines the payable on demand feature of checks and investment feature of savings accounts. A NOW account is functionally an interest paying checking account.

+ References

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Interest expense incurred on all savings account deposits.

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- Definition

The aggregate interest expense incurred on time deposits, including certificates of deposits, in domestic offices.

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Interest expense incurred on time deposits, including certificates of deposits, of $100,000 or more in domestic offices.

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Interest expense incurred on time deposits, including certificates of deposits, less than $100,000 in domestic offices.

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Amount of time deposits maturing after the fifth fiscal year following the latest fiscal year. Time deposits include, but are not limited to, certificates of deposits. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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Amount of time deposits maturing in the fifth fiscal year following the latest fiscal year. Time deposits include, but are not limited to, certificates of deposits. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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Amount of time deposits maturing in the fourth fiscal year following the latest fiscal year. Time deposits include, but are not limited to, certificates of deposits. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of time deposits maturing in the next fiscal year following the latest fiscal year. Time deposits include, but are not limited to, certificates of deposits. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of time deposits maturing in the third fiscal year following the latest fiscal year. Time deposits include, but are not limited to, certificates of deposits. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of time deposits maturing in the second fiscal year following the latest fiscal year. Time deposits include, but are not limited to, certificates of deposits. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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- Definition

The weighted average interest rate for domestic brokered deposit liabilities.

+ References

No definition available.

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