The Company and Summary of Significant Accounting Policies (Policies)	3 Months Ended
Mar. 31, 2022
Accounting Policies [Abstract]
Nature of Operations and Basis of Presentation	Nature of Operations and Basis of Presentation The Interim Consolidated Financial Statements contained herein include the accounts of Mercer International Inc. ("Mercer Inc.") and all of its subsidiaries (collectively the "Company"). Mercer Inc. owns 100% of its subsidiaries with the exception of the 50% joint venture interest in the Cariboo mill with West Fraser Mills Ltd., which is accounted for using the equity method. The Company's shares of common stock are quoted and listed for trading on the NASDAQ Global Select Market. The Interim Consolidated Financial Statements have been prepared by the Company pursuant to the rules and regulations of the United States Securities and Exchange Commission (the "SEC"). The year-end Consolidated Balance Sheet data was derived from audited financial statements. The footnote disclosure included herein has been prepared in accordance with accounting principles generally accepted for interim financial statements in the United States ("GAAP"). The unaudited Interim Consolidated Financial Statements should be read together with the audited Consolidated Financial Statements and accompanying notes included in the Company's latest Annual Report on Form 10‑K for the fiscal year ended December 31, 2021. In the opinion of the Company, the unaudited Interim Consolidated Financial Statements contained herein have been prepared on a consistent basis with the audited Consolidated Financial Statements and accompanying notes included in the Company's latest Annual Report on Form 10‑K for the fiscal year ended December 31, 2021 and contain all adjustments necessary for a fair statement of the results of the interim periods included. The results for the periods included herein may not be indicative of the results for the entire year. In these Interim Consolidated Financial Statements, unless otherwise indicated, all amounts are expressed in United States dollars ("U.S. dollars" or "$"). The symbol "€" refers to euros and the symbol "C$" refers to Canadian dollars.
Use of Estimates	Use of Estimates Preparation of financial statements and related disclosures in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant management judgment is required in determining the accounting for, among other things, pension and other post-retirement benefit obligations, deferred income taxes (valuation allowance and permanent reinvestment), depreciation and amortization, future cash flows associated with impairment testing for long-lived assets, the allocation of the purchase price in a business combination to the assets acquired and liabilities assumed, legal liabilities and contingencies. Actual results could differ materially from these estimates, and changes in these estimates are recorded when known.
Impact of the COVID-19 Pandemic	Impact of the COVID-19 Pandemic The Company is subject to risks and uncertainties as a result of the COVID-19 pandemic. During the pandemic, there have been several "waves" or periods during which there has been a significant widespread increase in reported infections and the emergence and rapid spread of new variants of the COVID-19 virus. In response to such waves, various countries have from time to time re-imposed various restrictions on social, business, travel and other activities. Such economic disruption could have a material adverse effect on the Company’s business. As of the date of issuance of these Interim Consolidated Financial Statements, the Company has not had significant downtime or closures at its mills or disruptions to raw material supplies or access to logistics networks due to the COVID-19 pandemic, but the extent to which the COVID-19 pandemic may materially impact the Company's future financial condition, liquidity, or results of operations remains uncertain. The Company’s future results of operations and liquidity, however, could be adversely impacted by economic factors arising from the pandemic that affect our business and customers. For instance, we may experience delays in payments of outstanding receivable amounts beyond normal payment terms, supply chain disruptions and uncertain demand, and the impact of any initiatives or programs that the Company may undertake to address financial and operational challenges faced by its customers.

The Company and Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2022

Nature of Operations and Basis of Presentation

The Interim Consolidated Financial Statements contained herein include the accounts of Mercer International Inc. ("Mercer Inc.") and all of its subsidiaries (collectively the "Company"). Mercer Inc. owns 100% of its subsidiaries with the exception of the 50% joint venture interest in the Cariboo mill with West Fraser Mills Ltd., which is accounted for using the equity method. The Company's shares of common stock are quoted and listed for trading on the NASDAQ Global Select Market.

The Interim Consolidated Financial Statements have been prepared by the Company pursuant to the rules and regulations of the United States Securities and Exchange Commission (the "SEC"). The year-end Consolidated Balance Sheet data was derived from audited financial statements. The footnote disclosure included herein has been prepared in accordance with accounting principles generally accepted for interim financial statements in the United States ("GAAP"). The unaudited Interim Consolidated Financial Statements should be read together with the audited Consolidated Financial Statements and accompanying notes included in the Company's latest Annual Report on Form 10‑K for the fiscal year ended December 31, 2021. In the opinion of the Company, the unaudited Interim Consolidated Financial Statements contained herein have been prepared on a consistent basis with the audited Consolidated Financial Statements and accompanying notes included in the Company's latest Annual Report on Form 10‑K for the fiscal year ended December 31, 2021 and contain all adjustments necessary for a fair statement of the results of the interim periods included. The results for the periods included herein may not be indicative of the results for the entire year.

In these Interim Consolidated Financial Statements, unless otherwise indicated, all amounts are expressed in United States dollars ("U.S. dollars" or "$"). The symbol "€" refers to euros and the symbol "C$" refers to Canadian dollars.

Use of Estimates

Preparation of financial statements and related disclosures in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Significant management judgment is required in determining the accounting for, among other things, pension and other post-retirement benefit obligations, deferred income taxes (valuation allowance and permanent reinvestment), depreciation and amortization, future cash flows associated with impairment testing for long-lived assets, the allocation of the purchase price in a business combination to the assets acquired and liabilities assumed, legal liabilities and contingencies. Actual results could differ materially from these estimates, and changes in these estimates are recorded when known.

Impact of the COVID-19 Pandemic

The Company is subject to risks and uncertainties as a result of the COVID-19 pandemic. During the pandemic, there have been several "waves" or periods during which there has been a significant widespread increase in reported infections and the emergence and rapid spread of new variants of the COVID-19 virus. In response to such waves, various countries have from time to time re-imposed various restrictions on social, business, travel and other activities. Such economic disruption could have a material adverse effect on the Company’s business.

As of the date of issuance of these Interim Consolidated Financial Statements, the Company has not had significant downtime or closures at its mills or disruptions to raw material supplies or access to logistics networks due to the COVID-19 pandemic, but the extent to which the COVID-19 pandemic may materially impact the Company's future financial condition, liquidity, or results of operations remains uncertain.

The Company’s future results of operations and liquidity, however, could be adversely impacted by economic factors arising from the pandemic that affect our business and customers. For instance, we may experience delays in payments of outstanding receivable amounts beyond normal payment terms, supply chain disruptions and uncertain demand, and the impact of any initiatives or programs that the Company may undertake to address financial and operational challenges faced by its customers.