Summary of Significant Accounting Policies (Policies)	9 Months Ended
Sep. 30, 2020
Accounting Policies [Abstract]
Use of Estimates [Policy Text Block]	Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (GAAP) requires management to make estimates and assumptions about future events. These estimates and the underlying assumptions affect the amounts of assets and liabilities reported, disclosures about contingent assets and liabilities, and reported amounts of revenues and expenses. Such estimates include the valuation of accounts receivable, inventories, goodwill, intangible assets, and other long-lived assets; legal contingencies; guarantee obligations; indemnifications; assumptions used in retirement, medical, and workers' compensation benefits; assumptions used in the determination of right-of-use assets and related lease liabilities; stock-based compensation; fair value measurements; income taxes; and vendor and customer rebates, among others. These estimates and assumptions are based on management's best estimates and judgment. Management evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors, including the current economic environment, which management believes to be reasonable under the circumstances. We adjust such estimates and assumptions when facts and circumstances dictate. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. Changes in these estimates resulting from continuing changes in the economic environment will be reflected in the consolidated financial statements in future periods.
Revenue Recognition [Policy Text Block]	Revenue Recognition Revenues are recognized when control of the promised goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. For revenue disaggregated by major product line for each reportable segment, see Note 12, Segment Information. Fees for shipping and handling charged to customers for sales transactions are included in "Sales" in our Consolidated Statements of Operations. When control over products has transferred to the customer, we have elected to recognize costs related to shipping and handling as fulfillment costs. For our Wood Products segment, costs related to shipping and handling are included in "Materials, labor, and other operating expenses (excluding depreciation)" in our Consolidated Statements of Operations. In our Wood Products segment, we view our shipping and handling costs as a cost of the manufacturing process and the movement of product to our end customers. For our Building Materials Distribution segment, costs related to shipping and handling of $49.2 million and $46.9 million, for the three months ended September 30, 2020 and 2019, respectively, and $134.1 million and $127.3 million for the nine months ended September 30, 2020 and 2019, respectively, are included in "Selling and distribution expenses" in our Consolidated Statements of Operations. In our Building Materials Distribution segment, our activities relate to the purchase and resale of finished product, and excluding shipping and handling costs from “Materials, labor, and other operating expenses (excluding depreciation)” provides us a clearer view of our operating performance and the effectiveness of our sales and purchasing functions. Customer Rebates and Allowances Rebates are provided to our customers and our customers' customers based on the volume of their purchases, among other factors such as customer loyalty, conversion, and commitment. We provide the rebates to increase the sell-through of our products. Rebates are generally estimated based on the expected amount to be paid and recorded as a decrease in "Sales." At September 30, 2020, and December 31, 2019, we had $62.7 million and $49.4 million, respectively, of rebates payable to our customers recorded in "Accrued liabilities, Other" on our Consolidated Balance Sheets. We adjust our estimate of revenue at the earlier of when the probability of rebates paid changes or when the amounts become fixed. There have not been significant changes to our estimates of rebates, although it is reasonably possible that a change in the estimate may occur.
Vendor Rebates and Allowances [Policy Text Block]	Rebates and allowances received from our vendors are recognized as a reduction of "Materials, labor, and other operating expenses (excluding depreciation)" when the product is sold, unless the rebates and allowances are linked to a specific incremental cost to sell a vendor's product. Amounts received from vendors that are linked to specific selling and distribution expenses are recognized as a reduction of "Selling and distribution expenses" in the period the expense is incurred.
Lessee, Leases [Policy Text Block]	Leases We primarily lease land, building, and equipment under operating and finance leases. We determine if an arrangement is a lease at inception and assess lease classification as either operating or finance at lease inception or upon modification. Substantially all of our leases with initial terms greater than one year are for real estate, including distribution centers, corporate headquarters, land, and other office space. Substantially all of these lease agreements have fixed payment terms based on the passage of time and are recorded in our Building Materials Distribution segment. Many of our leases include fixed escalation clauses, renewal options and/or termination options that are factored into our determination of lease term and lease payments when appropriate. Renewal options generally range from one to ten years with fixed payment terms similar to those in the original lease agreements. Some lease agreements provide us with the option to purchase the leased property at market value. Our lease agreements do not contain any residual value guarantees. Right-of-use (ROU) assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at the lease commencement date based on the estimated present value of fixed lease payments over the lease term. The current portion of our operating and finance lease liabilities are recorded in "Accrued liabilities, Other" on our Consolidated Balance Sheets. We use our estimated incremental borrowing rate, which is derived from information available at the lease commencement date, in determining the present value of lease payments. In determining our incremental borrowing rates, we give consideration to publicly available interest rates for instruments with similar characteristics, including credit rating, term, and collateralization. For purposes of determining straight-line rent expense, the lease term is calculated from the date we first take possession of the facility, including any periods of free rent and any renewal option periods we are reasonably certain of exercising. Variable lease expense generally includes reimbursement of actual costs for common area maintenance, property taxes, and insurance on leased real estate and are recorded as incurred. Most of our operating lease expense is recorded in "Selling and distribution expenses" in our Consolidated Statements of Operations. In addition, we do not separate lease and non-lease components for all of our leases. Our short-term leases primarily include equipment rentals with lease terms on a month-to-month basis, which provide for our seasonal needs and flexibility in the use of equipment. Our short-term leases also include certain real estate for which either party has the right to cancel upon providing notice of 30 to 90 days. We do not recognize ROU assets or lease liabilities for short-term leases.
Long-Lived Asset Impairment [Policy Text Block]	Long-Lived Asset Impairment We review long-lived assets for impairment when events or changes in circumstances indicate that the carrying amount of assets may not be recoverable (triggering event). An impairment of long-lived assets exists when the carrying value is not recoverable through future undiscounted cash flows from operations and when the carrying value of an asset or asset group exceeds its fair value.
Fair Value [Policy Text Block]	Fair Value Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The fair value hierarchy under GAAP gives the highest priority to quoted market prices (Level 1) and the lowest priority to unobservable inputs (Level 3). In general, and where applicable, we use quoted prices in active markets for identical assets or liabilities to determine fair value (Level 1). If quoted prices in active markets for identical assets or liabilities are not available to determine fair value, we use quoted prices for similar assets and liabilities or inputs that are observable either directly or indirectly (Level 2). If quoted prices for identical or similar assets are not available or are unobservable, we may use internally developed valuation models, whose inputs include bid prices, and third-party valuations utilizing underlying asset assumptions (Level 3).
Financial Instruments [Policy Text Block]	Financial Instruments Our financial instruments are cash and cash equivalents, accounts receivable, accounts payable, long-term debt, and interest rate swaps. Our cash is recorded at cost, which approximates fair value, and our cash equivalents are money market funds. As of September 30, 2020, and December 31, 2019, we held $466.0 million and $259.5 million, respectively, in money market funds that are measured at fair value on a recurring basis using Level 1 inputs. The recorded values of accounts receivable and accounts payable approximate fair values based on their short-term nature. At September 30, 2020, and December 31, 2019, the book value of our fixed-rate debt was $400.0 million and $350.0 million, respectively, and the fair value was estimated to be $430.0 million and $364.7 million, respectively. The difference between the book value and the fair value is derived from the difference between the period-end market interest rate and the stated rate of our fixed-rate, long-term debt. We estimated the fair value of our fixed-rate debt using quoted market prices of our debt in inactive markets (Level 2 inputs). The interest rate on our variable-rate debt is based on market conditions such as the London Interbank Offered Rate (LIBOR) or a base rate. Because the interest rate on the variable-rate debt is based on current market conditions, we believe that the estimated fair value of the outstanding balance on our variable-rate debt approximates book value. As discussed below, we also have interest rate swaps to mitigate our variable interest rate exposure, the fair value of which is measured based on Level 2 inputs.
Derivatives [Policy Text Block]	In accordance with our risk management strategy, we actively monitor our interest rate exposure and use derivative instruments from time to time to manage the related risk.
New and recently adopted accounting standards [Policy Text Block]	New and Recently Adopted Accounting Standards In March 2020, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides optional expedients and exceptions for applying generally accepted accounting principles (GAAP) to contracts, hedging relationships, and other transactions affected by reference rate reform if certain criteria are met. The amendments apply only to contracts, hedging relationships, and other transactions that reference LIBOR or another reference rate expected to be discontinued because of reference rate reform. Our current contracts that reference LIBOR include certain debt instruments and interest rate swaps. The amendments are effective for eligible contract modifications subsequent to March 12, 2020, and through December 31, 2022. The adoption of this standard did not have a material effect on our financial statements, but we will assess any eligible contract modifications in the future. In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which is intended to reduce complexity in accounting for income taxes. This ASU removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The updated guidance is effective for interim and annual reporting periods beginning after December 15, 2020, with early adoption permitted. We currently do not expect the adoption of the guidance to have a material effect on our financial statements, but will continue to monitor the standard through the effective date. In August 2018, the FASB issued ASU 2018-14, Compensation - Retirement Benefits - Defined Benefit Plans - General (Topic 715-20): Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans. This ASU amends ASC 715 to remove disclosures that are no longer considered cost beneficial, clarifies the specific requirements of disclosures, and adds disclosure requirements identified as relevant related to defined benefit pension and other postretirement plans. The ASU's changes related to disclosures are part of the FASB's disclosure framework project. The updated guidance is effective retrospectively for annual reporting periods ending after December 15, 2020, with early adoption permitted. We are currently evaluating the effects of this ASU on our disclosures in the notes to our financial statements. There were no other accounting standards recently issued that had or are expected to have a material impact on our consolidated financial statements and associated disclosures.
Compensation Related Costs [Policy Text Block]	We record compensation expense over the awards' vesting period and account for share-based award forfeitures as they occur, rather than making estimates of future forfeitures. Any shares not vested are forfeited. We recognize stock awards with only service conditions on a straight-line basis over the requisite service period.

Summary of Significant Accounting Policies (Policies)

9 Months Ended

Sep. 30, 2020

Use of Estimates The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America (GAAP) requires management to make estimates and assumptions about future events. These estimates and the underlying assumptions affect the amounts of assets and liabilities reported, disclosures about contingent assets and liabilities, and reported amounts of revenues and expenses. Such estimates include the valuation of accounts receivable, inventories, goodwill, intangible assets, and other long-lived assets; legal contingencies; guarantee obligations; indemnifications; assumptions used in retirement, medical, and workers' compensation benefits; assumptions used in the determination of right-of-use assets and related lease liabilities; stock-based compensation; fair value measurements; income taxes; and vendor and customer rebates, among others. These estimates and assumptions are based on management's best estimates and judgment. Management evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors, including the current economic environment, which management believes to be reasonable under the circumstances. We adjust such estimates and assumptions when facts and circumstances dictate. As future events and their effects cannot be determined with precision, actual results could differ significantly from these estimates. Changes in these estimates resulting from continuing changes in the economic environment will be reflected in the consolidated financial statements in future periods.

Revenue Recognition [Policy Text Block]

Revenue Recognition

Revenues are recognized when control of the promised goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. For revenue disaggregated by major product line for each reportable segment, see Note 12, Segment Information.

Fees for shipping and handling charged to customers for sales transactions are included in "Sales" in our Consolidated Statements of Operations. When control over products has transferred to the customer, we have elected to recognize costs related to shipping and handling as fulfillment costs. For our Wood Products segment, costs related to shipping and handling are included in "Materials, labor, and other operating expenses (excluding depreciation)" in our Consolidated Statements of Operations. In our Wood Products segment, we view our shipping and handling costs as a cost of the manufacturing process and the movement of product to our end customers. For our Building Materials Distribution segment, costs related to shipping and handling of $49.2 million and $46.9 million, for the three months ended September 30, 2020 and 2019, respectively, and $134.1 million and $127.3 million for the nine months ended September 30, 2020 and 2019, respectively, are included in "Selling and distribution expenses" in our Consolidated Statements of Operations. In our Building Materials Distribution segment, our activities relate to the purchase and resale of finished product, and excluding shipping and handling costs from “Materials, labor, and other operating expenses (excluding depreciation)” provides us a clearer view of our operating performance and the effectiveness of our sales and purchasing functions.

Customer Rebates and Allowances

Rebates are provided to our customers and our customers' customers based on the volume of their purchases, among other factors such as customer loyalty, conversion, and commitment. We provide the rebates to increase the sell-through of our products. Rebates are generally estimated based on the expected amount to be paid and recorded as a decrease in "Sales." At September 30, 2020, and December 31, 2019, we had $62.7 million and $49.4 million, respectively, of rebates payable to our customers recorded in "Accrued liabilities, Other" on our Consolidated Balance Sheets. We adjust our estimate of revenue at the earlier of when the probability of rebates paid changes or when the amounts become fixed. There have not been significant changes to our estimates of rebates, although it is reasonably possible that a change in the estimate may occur.

Vendor Rebates and Allowances [Policy Text Block]

Rebates and allowances received from our vendors are recognized as a reduction of "Materials, labor, and other operating expenses (excluding depreciation)" when the product is sold, unless the rebates and allowances are linked to a specific incremental cost to sell a vendor's product. Amounts received from vendors that are linked to specific selling and distribution expenses are recognized as a reduction of "Selling and distribution expenses" in the period the expense is incurred.

Lessee, Leases [Policy Text Block]

Leases

We primarily lease land, building, and equipment under operating and finance leases. We determine if an arrangement is a lease at inception and assess lease classification as either operating or finance at lease inception or upon modification. Substantially all of our leases with initial terms greater than one year are for real estate, including distribution centers, corporate headquarters, land, and other office space. Substantially all of these lease agreements have fixed payment terms based on the passage of time and are recorded in our Building Materials Distribution segment. Many of our leases include fixed escalation clauses, renewal options and/or termination options that are factored into our determination of lease term and lease payments when appropriate. Renewal options generally range from one to ten years with fixed payment terms similar to those in the original lease agreements. Some lease agreements provide us with the option to purchase the leased property at market value. Our lease agreements do not contain any residual value guarantees.

Right-of-use (ROU) assets represent our right to use an underlying asset for the lease term and lease liabilities represent our obligation to make lease payments arising from the lease. ROU assets and lease liabilities are recognized at the lease commencement date based on the estimated present value of fixed lease payments over the lease term. The current portion of our operating and finance lease liabilities are recorded in "Accrued liabilities, Other" on our Consolidated Balance Sheets.

We use our estimated incremental borrowing rate, which is derived from information available at the lease commencement date, in determining the present value of lease payments. In determining our incremental borrowing rates, we

give consideration to publicly available interest rates for instruments with similar characteristics, including credit rating, term, and collateralization.

For purposes of determining straight-line rent expense, the lease term is calculated from the date we first take possession of the facility, including any periods of free rent and any renewal option periods we are reasonably certain of exercising. Variable lease expense generally includes reimbursement of actual costs for common area maintenance, property taxes, and insurance on leased real estate and are recorded as incurred. Most of our operating lease expense is recorded in "Selling and distribution expenses" in our Consolidated Statements of Operations. In addition, we do not separate lease and non-lease components for all of our leases.

Our short-term leases primarily include equipment rentals with lease terms on a month-to-month basis, which provide for our seasonal needs and flexibility in the use of equipment. Our short-term leases also include certain real estate for which either party has the right to cancel upon providing notice of 30 to 90 days. We do not recognize ROU assets or lease liabilities for short-term leases.

Long-Lived Asset Impairment [Policy Text Block]

Long-Lived Asset Impairment We review long-lived assets for impairment when events or changes in circumstances indicate that the carrying amount of assets may not be recoverable (triggering event). An impairment of long-lived assets exists when the carrying value is not recoverable through future undiscounted cash flows from operations and when the carrying value of an asset or asset group exceeds its fair value.

Fair Value [Policy Text Block]

Fair Value

Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The fair value hierarchy under GAAP gives the highest priority to quoted market prices (Level 1) and the lowest priority to unobservable inputs (Level 3). In general, and where applicable, we use quoted prices in active markets for identical assets or liabilities to determine fair value (Level 1). If quoted prices in active markets for identical assets or liabilities are not available to determine fair value, we use quoted prices for similar assets and liabilities or inputs that are observable either directly or indirectly (Level 2). If quoted prices for identical or similar assets are not available or are unobservable, we may use internally developed valuation models, whose inputs include bid prices, and third-party valuations utilizing underlying asset assumptions (Level 3).

Financial Instruments [Policy Text Block]

Financial Instruments

Our financial instruments are cash and cash equivalents, accounts receivable, accounts payable, long-term debt, and interest rate swaps. Our cash is recorded at cost, which approximates fair value, and our cash equivalents are money market funds. As of September 30, 2020, and December 31, 2019, we held $466.0 million and $259.5 million, respectively, in money market funds that are measured at fair value on a recurring basis using Level 1 inputs. The recorded values of accounts receivable and accounts payable approximate fair values based on their short-term nature. At September 30, 2020, and December 31, 2019, the book value of our fixed-rate debt was $400.0 million and $350.0 million, respectively, and the fair value was estimated to be $430.0 million and $364.7 million, respectively. The difference between the book value and the fair value is derived from the difference between the period-end market interest rate and the stated rate of our fixed-rate, long-term debt. We estimated the fair value of our fixed-rate debt using quoted market prices of our debt in inactive markets (Level 2 inputs). The interest rate on our variable-rate debt is based on market conditions such as the London Interbank Offered Rate (LIBOR) or a base rate. Because the interest rate on the variable-rate debt is based on current market conditions, we believe that the estimated fair value of the outstanding balance on our variable-rate debt approximates book value. As discussed below, we also have interest rate swaps to mitigate our variable interest rate exposure, the fair value of which is measured based on Level 2 inputs.

Derivatives [Policy Text Block]

In accordance with our risk management strategy, we actively monitor our interest rate exposure and use derivative instruments from time to time to manage the related risk.

New and recently adopted accounting standards [Policy Text Block]

New and Recently Adopted Accounting Standards

In March 2020, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, which provides optional expedients and exceptions for applying generally accepted accounting principles (GAAP) to contracts, hedging relationships, and other transactions affected by reference rate reform if certain criteria are met. The amendments apply only to contracts, hedging relationships, and other transactions that reference LIBOR or another reference rate expected to be discontinued because of reference rate reform. Our current contracts that reference LIBOR include certain debt instruments and interest rate swaps. The amendments are effective for eligible contract modifications subsequent to March 12, 2020, and through December 31, 2022. The adoption of this standard did not have a material effect on our financial statements, but we will assess any eligible contract modifications in the future.

In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, which is intended to reduce complexity in accounting for income taxes. This ASU removes certain exceptions to the general principles in Topic 740 and also clarifies and amends existing guidance to improve consistent application. The updated guidance is effective for interim and annual reporting periods beginning after December 15, 2020, with early adoption permitted. We currently do not expect the adoption of the guidance to have a material effect on our financial statements, but will continue to monitor the standard through the effective date.

In August 2018, the FASB issued ASU 2018-14, Compensation - Retirement Benefits - Defined Benefit Plans - General (Topic 715-20): Disclosure Framework - Changes to the Disclosure Requirements for Defined Benefit Plans. This ASU amends ASC 715 to remove disclosures that are no longer considered cost beneficial, clarifies the specific requirements of disclosures, and adds disclosure requirements identified as relevant related to defined benefit pension and other postretirement plans. The ASU's changes related to disclosures are part of the FASB's disclosure framework project. The updated guidance is effective retrospectively for annual reporting periods ending after December 15, 2020, with early adoption permitted. We are currently evaluating the effects of this ASU on our disclosures in the notes to our financial statements.

There were no other accounting standards recently issued that had or are expected to have a material impact on our consolidated financial statements and associated disclosures.

We record compensation expense over the awards' vesting period and account for share-based award forfeitures as they occur, rather than making estimates of future forfeitures. Any shares not vested are forfeited. We recognize stock awards with only service conditions on a straight-line basis over the requisite service period.