Condensed consolidated interim financial statements Condensed consolidaed interim financial statements (Policies)	9 Months Ended
Sep. 30, 2021
Accounting Policies [Abstract]
Condensed consolidated interim financial statements	The unaudited condensed consolidated interim financial statements included in this report are prepared by the Company. In the opinion of management, all adjustments necessary for a fair presentation of the results of operations are reflected in these condensed consolidated interim financial statements. All significant intercompany accounts and transactions have been eliminated. The preparation of these financial statements requires management to make estimates and assumptions that affect the reported amounts of revenues, expenses, assets, liabilities, contingencies and noncontrolling interests subject to put provisions. The most significant estimates and assumptions underlying these financial statements and accompanying notes generally involve revenue recognition and accounts receivable, impairments of goodwill, accounting for income taxes, certain fair value estimates and loss contingencies. The results of operations reflected in these interim financial statements may not necessarily be indicative of annual operating results. These condensed consolidated interim financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 (2020 10-K). Prior period classifications have been conformed to the current period presentation. The Company has evaluated subsequent events through the date these condensed consolidated interim financial statements were issued and has included all necessary adjustments and disclosures.
Earnings Per Share	Basic earnings per share is calculated by dividing net income attributable to the Company by the weighted average number of common shares outstanding. Weighted average common shares outstanding include restricted stock unit awards that are no longer subject to forfeiture because the recipients have satisfied either the explicit vesting terms or retirement eligibility requirements. Diluted earnings per share includes the dilutive effect of outstanding stock-settled stock appreciation rights and unvested stock units as computed under the treasury stock method.
Short-term and Long-term Investments	Debt securities: The Company's short-term debt investments are principally bank certificates of deposit with contractual maturities longer than three months but shorter than one year. These debt securities are accounted for as held to maturity and recorded at amortized cost, which approximated their fair values at September 30, 2021 and December 31, 2020.Equity securities: During the nine months ended September 30, 2021 certain of the Company’s equity investments previously accounted for under the adjusted cost method now have readily determinable fair values from public markets. As a result, these investments were reclassified from equity method and other investments to short-term investments during that period.
Long-term debt	These cap agreements are designated as cash flow hedges and, as a result, changes in the fair values of the cap agreements are reported in other comprehensive income. The original premiums paid for the caps are amortized to debt expense on a straight-line basis over the term of each cap agreement starting from its effective date.
Accumulated other comprehensive Income	The interest rate cap agreement net realized losses reclassified into net income are recorded as debt expense in the corresponding consolidated statements of income.
Fair Value of Financial Instruments	Interest rate cap agreements are recorded at fair value estimated from valuation models utilizing the income approach and commonly accepted valuation techniques that use inputs from closing prices for similar assets and liabilities in active markets as well as other relevant observable market inputs at quoted intervals such as current interest rates, forward yield curves, implied volatility and credit default swap pricing. The Company does not believe the ultimate amount that could be realized upon settlement of these interest rate cap agreements would be materially different from the fair value estimates currently reported. See Note 8 for further discussion.The estimated fair value measurements of contingent earn-out obligations are primarily based on unobservable inputs, including projected earnings before interest, taxes, depreciation, and amortization (EBITDA), revenue and certain operating metrics. The estimated fair values of these contingent earn-out obligations are remeasured as of each reporting date and could fluctuate based upon any significant changes in key assumptions, such as changes in the Company's credit risk adjusted rate that is used to discount obligations to present value.
New Accounting Standards	New standards recently adopted In December 2019, the FASB issued Accounting Standards Update (ASU) No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. ASU No. 2019-12 attempts to simplify aspects of accounting for franchise taxes and enacted changes in tax laws or rates, and clarifies the accounting for transactions that result in a step-up in the tax basis of goodwill. The amendments in this ASU became effective for the Company beginning on January 1, 2021. The adoption of ASU No. 2019-12 did not have a material impact on the Company's consolidated financial statements. New standards not yet adopted In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting. ASU No. 2020-04 provides optional expedients and exceptions for applying U.S. generally accepted accounting principles to contract modifications and hedging relationships, subject to certain criteria, that reference LIBOR or another rate that is expected to be discontinued. The amendments in this ASU were effective beginning on March 12, 2020, and the Company may elect to apply the amendments prospectively through December 31, 2022. The Company is currently assessing the effect this guidance may have on its consolidated financial statements.

Condensed consolidated interim financial statements Condensed consolidaed interim financial statements (Policies)

9 Months Ended

Sep. 30, 2021

Condensed consolidated interim financial statements

The unaudited condensed consolidated interim financial statements included in this report are prepared by the Company. In the opinion of management, all adjustments necessary for a fair presentation of the results of operations are reflected in these condensed consolidated interim financial statements. All significant intercompany accounts and transactions have been eliminated. The preparation of these financial statements requires management to make estimates and assumptions that affect the reported amounts of revenues, expenses, assets, liabilities, contingencies and noncontrolling interests subject to put provisions. The most significant estimates and assumptions underlying these financial statements and accompanying notes generally involve revenue recognition and accounts receivable, impairments of goodwill, accounting for income taxes, certain fair value estimates and loss contingencies. The results of operations reflected in these interim financial statements may not necessarily be indicative of annual operating results. These condensed consolidated interim financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 (2020 10-K). Prior period classifications have been conformed to the current period presentation. The Company has evaluated subsequent events through the date these condensed consolidated interim financial statements were issued and has included all necessary adjustments and disclosures.

Earnings Per Share

Basic earnings per share is calculated by dividing net income attributable to the Company by the weighted average number of common shares outstanding. Weighted average common shares outstanding include restricted stock unit awards that are no longer subject to forfeiture because the recipients have satisfied either the explicit vesting terms or retirement eligibility requirements.

Diluted earnings per share includes the dilutive effect of outstanding stock-settled stock appreciation rights and unvested stock units as computed under the treasury stock method.

Short-term and Long-term Investments

Debt securities: The Company's short-term debt investments are principally bank certificates of deposit with contractual maturities longer than three months but shorter than one year. These debt securities are accounted for as held to maturity and recorded at amortized cost, which approximated their fair values at September 30, 2021 and December 31, 2020.Equity securities: During the nine months ended September 30, 2021 certain of the Company’s equity investments previously accounted for under the adjusted cost method now have readily determinable fair values from public markets. As a result, these investments were reclassified from equity method and other investments to short-term investments during that period.

Long-term debt

These cap agreements are designated as cash flow hedges and, as a result, changes in the fair values of the cap agreements are reported in other comprehensive income. The original premiums paid for the caps are amortized to debt expense on a straight-line basis over the term of each cap agreement starting from its effective date.

Accumulated other comprehensive Income

The interest rate cap agreement net realized losses reclassified into net income are recorded as debt expense in the corresponding consolidated statements of income.

Fair Value of Financial Instruments

Interest rate cap agreements are recorded at fair value estimated from valuation models utilizing the income approach and commonly accepted valuation techniques that use inputs from closing prices for similar assets and liabilities in active markets as well as other relevant observable market inputs at quoted intervals such as current interest rates, forward yield curves, implied volatility and credit default swap pricing. The Company does not believe the ultimate amount that could be realized upon settlement of these interest rate cap agreements would be materially different from the fair value estimates currently reported. See Note 8 for further discussion.The estimated fair value measurements of contingent earn-out obligations are primarily based on unobservable inputs, including projected earnings before interest, taxes, depreciation, and amortization (EBITDA), revenue and certain operating metrics. The estimated fair values of these contingent earn-out obligations are remeasured as of each reporting date and could fluctuate based upon any significant changes in key assumptions, such as changes in the Company's credit risk adjusted rate that is used to discount obligations to present value.

New Accounting Standards

New standards recently adopted

In December 2019, the FASB issued Accounting Standards Update (ASU) No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. ASU No. 2019-12 attempts to simplify aspects of accounting for franchise taxes and enacted changes in tax laws or rates, and clarifies the accounting for transactions that result in a step-up in the tax basis of goodwill. The amendments in this ASU became effective for the Company beginning on January 1, 2021. The adoption of ASU No. 2019-12 did not have a material impact on the Company's consolidated financial statements.

New standards not yet adopted

In March 2020, the FASB issued ASU No. 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting. ASU No. 2020-04 provides optional expedients and exceptions for applying U.S. generally accepted accounting principles to contract modifications and hedging relationships, subject to certain criteria, that reference LIBOR or another rate that is expected to be discontinued. The amendments in this ASU were effective beginning on March 12, 2020, and the Company may elect to apply the amendments prospectively through December 31, 2022. The Company is currently assessing the effect this guidance may have on its consolidated financial statements.