Condensed consolidated interim financial statements Condensed consolidaed interim financial statements (Policies)	3 Months Ended
Mar. 31, 2020
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 assets, liabilities, revenues and expenses. 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 for the three months ended March 31, 2020 are not necessarily indicative of the operating results for the full year. 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, 2019 (10-K). Prior year balances and amounts have been reclassified to conform to the current year 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 March 31, 2020 and December 31, 2019. Equity securities: The Company's equity investments in mutual funds and common stock are held within a trust to fund existing obligations associated with several of the Company’s non-qualified deferred compensation plans.
Income Taxes	The Company recognizes accrued interest and penalties related to unrecognized tax benefits in its income tax expense.
Long-term debt	The cap agreements are designated as cash flow hedges and, as a result, changes in the fair values of these cap agreements are reported in other comprehensive income. The amortization of the original cap premium is recognized as a component of debt expense on a straight-line basis over the terms of the cap agreements.
Long-term incentive compensation	The Company’s stock-based compensation expense for stock-settled awards is measured at the estimated fair value of awards on the date of grant and recognized on a cumulative straight-line basis over the vesting terms of the awards unless the stock awards are based on non-market based performance metrics, in which case expense is adjusted for the expected ultimate shares to be issued as of the end of each reporting period. Stock-based compensation expense for cash-settled awards is based on their estimated fair values as of the end of each reporting period. The expense for all stock-based awards is recognized net of expected forfeitures.
Accumulated other comprehensive Income	The reclassification of net cap realized losses into 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 to these condensed consolidated financial statements 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) and revenue. The estimated fair value of these contingent earn-out obligations is 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 June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The amendments in this ASU amend the impairment model to utilize an expected loss methodology in place of the incurred loss methodology for financial instruments and off-balance sheet credit exposures. The amendment requires entities to consider a broader range of information to estimate expected credit losses, which may result in earlier recognition of losses. The amendments in this ASU became effective for the Company beginning on January 1, 2020 and were applied using a modified retrospective basis. The adoption of ASU No. 2016-13 did not have a material impact on the Company's consolidated financial statements. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework -Changes to the Disclosure Requirements for Fair Value Measurement. The applicable amendments in this ASU remove requirements for disclosures concerning transfers between fair value measurement levels 1, 2 and 3 and disclosures concerning valuation processes for level 3 fair value measurements. The applicable amendments in this ASU also add a requirement to separately disclose the changes in unrealized gains and losses included in other comprehensive income for the reporting period for level 3 items measured at fair value on a recurring basis, and require disclosure of the range and weighted average of significant unobservable inputs used to develop level 3 fair value measurements. The amendments in this ASU became effective for the Company beginning on January 1, 2020 and were applied on a prospective basis. The adoption of this ASU did not have a material impact on the Company’s consolidated financial statements when adopted January 1, 2020. In August 2018, the FASB issued ASU No. 2018-15, Intangibles-Goodwill and Other-Internal Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. ASU No. 2018-15 aligns the requirements for capitalizing implementation costs incurred in a cloud computing arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The Company adopted this ASU as of January 1, 2020, using the prospective transition approach, which allows the Company to change the accounting method without restating prior periods or booking cumulative adjustments. The adoption of ASU No. 2018-15 did not have a material impact on the Company's consolidated financial statements. New standards not yet adopted In December 2019, the FASB issued 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. ASU No. 2019-12 is effective for public business entities for fiscal years beginning after December 15, 2020, including interim periods within that fiscal year. Early adoption is permitted for all entities. The Company is currently assessing the effect this guidance may have on its consolidated financial statements. 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 (GAAP) to contract modifications and hedging relationships, subject to meeting 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)

3 Months Ended

Mar. 31, 2020

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 assets, liabilities, revenues and expenses. 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 for the three months ended March 31, 2020 are not necessarily indicative of the operating results for the full year. 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, 2019 (10-K). Prior year balances and amounts have been reclassified to conform to the current year 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 March 31, 2020 and December 31, 2019.

Equity securities: The Company's equity investments in mutual funds and common stock are held within a trust to fund existing obligations associated with several of the Company’s non-qualified deferred compensation plans.

Income Taxes

The Company recognizes accrued interest and penalties related to unrecognized tax benefits in its income tax expense.

Long-term debt

The cap agreements are designated as cash flow hedges and, as a result, changes in the fair values of these cap agreements are reported in other comprehensive income. The amortization of the original cap premium is recognized as a component of debt expense on a straight-line basis over the terms of the cap agreements.

Long-term incentive compensation

The Company’s stock-based compensation expense for stock-settled awards is measured at the estimated fair value of awards on the date of grant and recognized on a cumulative straight-line basis over the vesting terms of the awards unless the stock awards are based on non-market based performance metrics, in which case expense is adjusted for the expected ultimate shares to be issued as of the end of each reporting period. Stock-based compensation expense for cash-settled awards is based on their estimated fair values as of the end of each reporting period. The expense for all stock-based awards is recognized net of expected forfeitures.

Accumulated other comprehensive Income

The reclassification of net cap realized losses into 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 to these condensed consolidated financial statements 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) and revenue. The estimated fair value of these contingent earn-out obligations is 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 June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The amendments in this ASU amend the impairment model to utilize an expected loss methodology in place of the incurred loss methodology for financial instruments and off-balance sheet credit exposures. The amendment requires entities to consider a broader range of information to estimate expected credit losses, which may result in earlier recognition of losses. The amendments in this ASU became effective for the Company beginning on January 1, 2020 and were applied using a modified retrospective basis. The adoption of ASU No. 2016-13 did not have a material impact on the Company's consolidated financial statements.

In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework -Changes to the Disclosure Requirements for Fair Value Measurement. The applicable amendments in this ASU remove requirements for disclosures concerning transfers between fair value measurement levels 1, 2 and 3 and disclosures concerning valuation processes for level 3 fair value measurements. The applicable amendments in this ASU also add a requirement to separately disclose the changes in unrealized gains and losses included in other comprehensive income for the reporting period for level 3 items measured at fair value on a recurring basis, and require disclosure of the range and weighted average of significant unobservable inputs used to develop level 3 fair value measurements. The amendments in this ASU became effective for the Company beginning on January 1, 2020 and were applied on a prospective basis. The adoption of this ASU did not have a material impact on the Company’s consolidated financial statements when adopted January 1, 2020.

In August 2018, the FASB issued ASU No. 2018-15, Intangibles-Goodwill and Other-Internal Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. ASU No. 2018-15 aligns the requirements for capitalizing implementation costs incurred in a cloud computing arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The Company adopted this ASU as of January 1, 2020, using the prospective transition approach, which allows the Company to change the accounting method without restating prior periods or booking cumulative adjustments. The adoption of ASU No. 2018-15 did not have a material impact on the Company's consolidated financial statements.

New standards not yet adopted

In December 2019, the FASB issued 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. ASU No. 2019-12 is effective for public business entities for fiscal years beginning after December 15, 2020, including interim periods within that fiscal year. Early adoption is permitted for all entities. The Company is currently assessing the effect this guidance may have on its consolidated financial statements.

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 (GAAP) to contract modifications and hedging relationships, subject to meeting 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.