Loans (Policies)	6 Months Ended
Loans (Policies)	Jun. 30, 2011
Loans [Abstract]
Allowances for Credit Losses	BOK Financial maintains separate allowances for loan losses and for off-balance sheet credit risk related to commitments to extend credit and standby letters of credit. As discussed in greater detail in Note 5, the Company also has separate allowances related to off-balance sheet credit risk related to residential mortgage loans sold with full or partial recourse and for residential mortgage loans sold to government sponsored agencies under standard representation and warranties. The allowance for loan losses is assessed by management on a quarterly basis and consists of specific amounts attributed to certain impaired loans, general allowances based on migration factors for unimpaired loans and non-specific allowances based on general economic conditions, risk concentration and related factors. Impairment is individually measured for certain impaired loans and collectively measured for all other loans. There have been no material changes in the approach or techniques utilized in developing the allowances for loan losses and off-balance sheet credit losses. Internally risk graded loans are evaluated individually for impairment. Non-risk graded loans are collectively evaluated for impairment through past-due status and other relevant factors. Substantially all commercial and commercial real estate loans are risk graded. Certain residential mortgage and consumer loans are also risk graded. Certain commercial loans and most residential mortgage and consumer loans are small balance, homogeneous pools of loans that are not risk graded. Loans are considered to be impaired when it becomes probable that BOK Financial will be unable to collect all amounts due according to the contractual terms of the loan agreements. This is substantially the same criteria used to determine when a loan should be placed on nonaccrual status. Specific allowances for impaired loans are measured by an evaluation of estimated future cash flows discounted at the loans' initial effective interest rate or the fair value of collateral for certain collateral dependent loans. Historical statistics may be used in limited situation to assist in estimating future cash flows or collateral values, such as when an impaired collateral dependent loan is identified at the end of a reporting period. Historical statistics are a practical way to estimate impairment until an updated appraisal of collateral value is received or a full assessment of future cash flows is completed. Estimates of future cash flows and collateral value require significant judgments and are subject to volatility. General allowances for unimpaired loans are based on migration models. Separate migration models are used to determine general allowances for commercial and commercial real estate loans, residential mortgage loans and consumer loans. All commercial and commercial real estate loans are risk-graded based on an evaluation of the borrowers' ability to repay. Risk grades are updated quarterly. Migration factors are determined for each risk grade to determine the inherent loss based on historical trends. An eight-quarter aggregate accumulation of net losses is used as a basis for the migration factors. Losses incurred in more recent periods are more heavily weighted by a sum-of-periods-digits formula. The higher of the current loss factors based on migration trends or a minimum migration factor based upon long-term history is assigned to each risk grade. The resulting general allowances may be adjusted upward or downward by management to account for the limitations in migration models which are based entirely on historical data, such as their limited accuracy at the beginning and ending of credit cycles. The general allowance for residential mortgage loans is based on an eight-quarter average percent of loss. The general allowance for consumer loans is based on an eight-quarter average percent loss with separate migration factors determined by major product line, such as indirect automobile loans and direct consumer loans. Nonspecific allowances are maintained for risks beyond factors specific to a particular loan or identified by the migration models. These factors include trends in the economy in our primary lending areas, conditions in certain industries where we have a concentration and overall growth in the loan portfolio. Evaluation of nonspecific factors considers the effect of the duration of the business cycle on migration factors and also considers current economic conditions and other factors. A provision for credit losses is charged against earnings in amounts necessary to maintain appropriate allowances for loan and off-balance sheet credit losses. Loans are charged off when the loan balance or a portion of the loan balance is no longer covered by the paying capacity of the borrower based on an evaluation of available cash resources and collateral value. Loans are evaluated quarterly and charge-offs are taken in the quarter in which the loss is identified. Additionally, all unsecured or under-secured residential mortgage and consumer loans that are past due 180 days are charged off. Recoveries of loans previously charged off are added to the allowance. Collateral value of real property is generally based on third party appraisals that conform to Uniform Standards of Professional Appraisal Practice, less estimated selling costs. Appraised values are on an “as-is” basis and are not adjusted by the Company. Collateral value of mineral rights is generally determined by our internal staff of engineers based on projected cash flows from proven oil and gas reserves under existing economic and operating conditions. The value of other collateral is generally determined by our special assets staff based on projected liquidation cash flows under current market conditions. Collateral values and available cash resources that support impaired loans are evaluated quarterly. Updated appraisals are obtained at least annually or more frequently if market conditions indicate collateral values have declined.
Loans Policy	Loans are either secured or unsecured based on the type of loan and the financial condition of the borrower. Repayment is generally expected from cash flow or proceeds from the sale of selected assets of the borrower. BOK Financial is exposed to risk of loss on loans due to the borrower's difficulties, which may arise from any number of factors, including problems within the respective industry or local economic conditions. Access to collateral, in the event of borrower default, is reasonably assured through adherence to applicable lending laws and through sound lending standards and credit review procedures. Performing loans may be renewed under then current collateral value, debt service ratio and other underwriting standards. Nonperforming loans may be renewed and will remain on nonaccrual status. Nonperforming loans renewed will be evaluated and may be charged off if the loan balance is no longer covered by the paying capacity of the borrower based on an evaluation of available cash resources and collateral value. Interest is accrued at the applicable interest rate on the principal amount outstanding. Loans are placed on nonaccrual status when, in the opinion of management, full collection of principal or interest is uncertain. Interest previously accrued but not collected is charged against interest income when the loan is placed on nonaccrual status. Payments on nonaccrual loans are applied to principal or reported as interest income, according to management's judgment as to the collectability of principal. Loans may be returned to accruing status when, in the opinion of management, full collection of principal and interest, including principal previously charged off, is probable based on improvements in the borrower's financial condition or a sustained period of performance. Loan origination and commitment fees and direct loan acquisition and origination costs are deferred and amortized as an adjustment to yield over the life of the loan or over the commitment period, as applicable. Certain residential mortgage loans originated by the Company are held for sale. All residential mortgage loans originated for sale are carried at fair value based on sales commitments or market quotes. Changes in fair value are recorded in other operating revenue – mortgage banking revenue.