Basis of Presentation and Principles of Consolidation	9 Months Ended
Sep. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The accompanying unaudited condensed consolidated balance sheet as of September 30, 2015, the unaudited condensed consolidated statements of operations and comprehensive income for the three and nine months ended September 30, 2015 and 2014, and the unaudited condensed consolidated statements of cash flows for the nine months ended September 30, 2015 and 2014, have been prepared on the same basis as the Company’s audited consolidated financial statements and include all adjustments necessary for the fair presentation of its consolidated results of operations, financial position, comprehensive income and cash flows. Results for the interim periods are not necessarily indicative of results to be expected for the full year or any other future periods. The condensed consolidated balance sheet as of December 31, 2014 has been derived from the Company’s audited financial statements, which are included in its 2014 Annual Report on Form 10-K, filed with the Securities and Exchange Commission (“SEC”) on March 2, 2015. The significant accounting policies and certain financial information that are normally included in financial statements prepared in accordance with accounting principles generally accepted in the U.S. (“GAAP”), but which are not required for interim reporting purposes, have been omitted. The unaudited condensed consolidated interim financial statements should be read in conjunction with the Company’s audited consolidated financial statements in its Annual Report on Form 10-K, for the year ended December 31, 2014. The unaudited condensed consolidated financial statements include Core-Mark and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in the unaudited condensed consolidated financial statements. Concentration of Credit Risks Financial instruments, which potentially subject the Company to concentrations of credit risk, consist principally of cash investments, accounts receivable and other receivables. The Company places its cash and cash equivalents in short-term instruments with high quality financial institutions and limits the amount of credit exposure in any one financial instrument. The Company pursues amounts and incentives due from vendors in the normal course of business and is often allowed to deduct these amounts and incentives from payments made to vendors. A credit review is completed for new customers and ongoing credit evaluations of each customer’s financial condition are performed periodically, with reserves maintained for potential credit losses. Credit limits given to customers are based on a risk assessment of their ability to pay and other factors. Accounts receivable are typically not collateralized, but the Company may require prepayments or other guarantees whenever deemed necessary. Alimentation Couche-Tard, Inc. (“Couche-Tard”), the Company’s largest customer, accounted for approximately 13.8% and 14.3% of the Company’s total net sales in the three and nine months ended September 30, 2015, respectively, and accounted for approximately 14.6% of the Company's net sales for both the three and nine months ended September 30, 2014. No single customer accounted for 10% or more of the Company’s accounts receivables as of September 30, 2015 or December 31, 2014. Recent Accounting Standards or Updates Not Yet Effective On May 28, 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers: Topic 606 (“ASU 2014-09”), to supersede nearly all existing revenue recognition guidance under U.S. GAAP. The core principle of ASU 2014-09 is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. On August 12, 2015, the FASB issued ASU 2015-14 to defer the effective date of the new revenue recognition standard for annual reports on fiscal years beginning after December 15, 2017. The Company is currently evaluating the impact of the adoption of ASU 2014-09 on its financial statements. On May 7, 2015, the FASB issued ASU No. 2015-07, Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or Its Equivalent): Topic 820 (“ASU 2015-07”). The standard removes the requirement to categorize within the fair value hierarchy all investments for which fair value is measured using the net asset value per share practical expedient. The Company does not hold any such investments on its condensed consolidated balance sheet, however, the assets held in a group trust for the Company’s defined benefit pension plan include such investments. ASU 2015-07 requires retrospective adoption and is effective for the Company beginning in 2016, although early adoption is permitted. The Company is currently evaluating the impact ASU 2015-07 will have on its financial statements. On August 18, 2015, the FASB issued ASU No. 2015-15, Imputation of Interest: Presentation and Subsequent Measurement of Debt Issuance Costs Associated with Line-of -Credit Arrangements: Subtopic 835-30 (“ASU 2015-15”). The guidance states that the SEC staff would not object to an entity deferring and presenting debt issuance costs as an asset and subsequently amortizing the deferred debt issuance costs ratably over the term of the line-of-credit arrangement, regardless of whether there are any outstanding borrowings on the line-of-credit arrangement. ASU 2015-15 requires retrospective application and is effective for annual periods beginning after December 15, 2015. The Company has determined the adoption of ASU 2015-15 will not have a material impact on its financial statements. On September 25, 2015, the FASB issued ASU 2015-16, Business Combinations (Topic 805): Simplifying the Accounting for Measurement-Period Adjustments (“ASU 2015-16”). The new guidance eliminates the requirement that an acquiring entity in a business combination account for measurement-period adjustments retrospectively. Under ASU 2015-16, acquirers must recognize measurement-period adjustments in the period in which they determine the amounts, including the effect on earnings of any amounts they would have recorded in previous periods, if the accounting had been completed at the acquisition date. The amendments in this update are to be applied prospectively, for fiscal years beginning after December 15, 2015. The Company has determined the adoption of ASU 2015-16 will not have a material impact on its financial statements.

Basis of Presentation and Principles of Consolidation

The accompanying unaudited condensed consolidated balance sheet as of September 30, 2015, the unaudited condensed consolidated statements of operations and comprehensive income for the three and nine months ended September 30, 2015 and 2014, and the unaudited condensed consolidated statements of cash flows for the nine months ended September 30, 2015 and 2014, have been prepared on the same basis as the Company’s audited consolidated financial statements and include all adjustments necessary for the fair presentation of its consolidated results of operations, financial position, comprehensive income and cash flows. Results for the interim periods are not necessarily indicative of results to be expected for the full year or any other future periods. The condensed consolidated balance sheet as of December 31, 2014 has been derived from the Company’s audited financial statements, which are included in its 2014 Annual Report on Form 10-K, filed with the Securities and Exchange Commission (“SEC”) on March 2, 2015.

The significant accounting policies and certain financial information that are normally included in financial statements prepared in accordance with accounting principles generally accepted in the U.S. (“GAAP”), but which are not required for interim reporting purposes, have been omitted. The unaudited condensed consolidated interim financial statements should be read in conjunction with the Company’s audited consolidated financial statements in its Annual Report on Form 10-K, for the year ended December 31, 2014.

The unaudited condensed consolidated financial statements include Core-Mark and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in the unaudited condensed consolidated financial statements.

Concentration of Credit Risks

Financial instruments, which potentially subject the Company to concentrations of credit risk, consist principally of cash investments, accounts receivable and other receivables. The Company places its cash and cash equivalents in short-term instruments with high quality financial institutions and limits the amount of credit exposure in any one financial instrument. The Company pursues amounts and incentives due from vendors in the normal course of business and is often allowed to deduct these amounts and incentives from payments made to vendors.

A credit review is completed for new customers and ongoing credit evaluations of each customer’s financial condition are performed periodically, with reserves maintained for potential credit losses. Credit limits given to customers are based on a risk assessment of their ability to pay and other factors. Accounts receivable are typically not collateralized, but the Company may require prepayments or other guarantees whenever deemed necessary.

Alimentation Couche-Tard, Inc. (“Couche-Tard”), the Company’s largest customer, accounted for approximately 13.8% and 14.3% of the Company’s total net sales in the three and nine months ended September 30, 2015, respectively, and accounted for approximately 14.6% of the Company's net sales for both the three and nine months ended September 30, 2014. No single customer accounted for 10% or more of the Company’s accounts receivables as of September 30, 2015 or December 31, 2014.

Recent Accounting Standards or Updates Not Yet Effective

On May 28, 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers: Topic 606 (“ASU 2014-09”), to supersede nearly all existing revenue recognition guidance under U.S. GAAP. The core principle of ASU 2014-09 is to recognize revenues when promised goods or services are transferred to customers in an amount that reflects the consideration that is expected to be received for those goods or services. On August 12, 2015, the FASB issued ASU 2015-14 to defer the effective date of the new revenue recognition standard for annual reports on fiscal years beginning after December 15, 2017. The Company is currently evaluating the impact of the adoption of ASU 2014-09 on its financial statements.

On May 7, 2015, the FASB issued ASU No. 2015-07, Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or Its Equivalent): Topic 820 (“ASU 2015-07”). The standard removes the requirement to categorize within the fair value hierarchy all investments for which fair value is measured using the net asset value per share practical expedient. The Company does not hold any such investments on its condensed consolidated balance sheet, however, the assets held in a group trust for the Company’s defined benefit pension plan include such investments. ASU 2015-07 requires retrospective adoption and is effective for the Company beginning in 2016, although early adoption is permitted. The Company is currently evaluating the impact ASU 2015-07 will have on its financial statements.

On August 18, 2015, the FASB issued ASU No. 2015-15, Imputation of Interest: Presentation and Subsequent Measurement of Debt Issuance Costs Associated with Line-of -Credit Arrangements: Subtopic 835-30 (“ASU 2015-15”). The guidance states that the SEC staff would not object to an entity deferring and presenting debt issuance costs as an asset and subsequently amortizing the deferred debt issuance costs ratably over the term of the line-of-credit arrangement, regardless of whether there are any outstanding borrowings on the line-of-credit arrangement. ASU 2015-15 requires retrospective application and is effective for annual periods beginning after December 15, 2015. The Company has determined the adoption of ASU 2015-15 will not have a material impact on its financial statements.

On September 25, 2015, the FASB issued ASU 2015-16, Business Combinations (Topic 805): Simplifying the Accounting for Measurement-Period Adjustments (“ASU 2015-16”). The new guidance eliminates the requirement that an acquiring entity in a business combination account for measurement-period adjustments retrospectively. Under ASU 2015-16, acquirers must recognize measurement-period adjustments in the period in which they determine the amounts, including the effect on earnings of any amounts they would have recorded in previous periods, if the accounting had been completed at the acquisition date. The amendments in this update are to be applied prospectively, for fiscal years beginning after December 15, 2015. The Company has determined the adoption of ASU 2015-16 will not have a material impact on its financial statements.