Condensed consolidated interim financial statements Condensed consolidaed interim financial statements (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Condensed consolidated interim financial statements	The condensed consolidated interim financial statements included in this report are prepared by the Company without audit. 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, contingencies, impairments of goodwill and investments, accounting for income taxes, long-term variable compensation accruals, consolidation of variable interest entities and certain fair value estimates. The results of operations for the nine months ended September 30, 2018 are not necessarily indicative of the operating results for the full year. The 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, 2017. 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 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, adjusted for any change in noncontrolling interest redemption rights in excess of fair value, by the weighted average number of common shares, net of the weighted average shares held in escrow that under certain circumstances may have been returned to the Company. Diluted earnings per share includes the dilutive effect of outstanding stock-settled stock appreciation rights (SSARs) and unvested stock units (under the treasury stock method) as well as the weighted average shares held in escrow that were outstanding during the period.
Short-term and Long-term Investments	From January 1, 2018, equity securities that have readily determinable fair values or redemption values are recorded at estimated fair value with changes in their value recognized in current earnings. The Company classifies its debt securities as held-to-maturity and records them at amortized cost based on its intentions and strategy concerning those investments. The Company classifies these debt and equity investments as "Short-term investments" or "Long-term investments" on its consolidated balance sheet, as applicable, based on the characteristics of the financial instrument or the Company's intentions or expectations for the investment.
Income Taxes	The Company recognizes accrued interest and penalties related to unrecognized tax benefits in its income tax expense.
Long-term debt	the Company maintains several effective interest rate cap agreements that have the economic effect of capping the Company's maximum exposure to LIBOR variable interest rate changes on specific portions of the Company's floating rate debt, as described below. 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. These cap agreements do not contain credit-risk contingent features.
Noncontrolling interest subject to put provisions and other commitments	The Company has potential obligations to purchase the equity interests held by third parties in several of its majority-owned joint ventures and other nonconsolidated entities. These obligations are in the form of put provisions that are exercisable at the third-party owners’ discretion within specified periods as outlined in each specific put provision. If these put provisions were exercised, the Company would be required to purchase the third-party owners’ equity interests at either the appraised fair market value or a predetermined multiple of earnings or cash flows attributable to the equity interests put to the Company, which is intended to approximate fair value. The methodology the Company uses to estimate the fair values of noncontrolling interests subject to put provisions assumes the higher of either a liquidation value of net assets or an average multiple of earnings, based on historical earnings, patient mix and other performance indicators that can affect future results, as well as other factors. The estimated fair values of noncontrolling interests subject to put provisions are a critical accounting estimate that involves significant judgments and assumptions and may not be indicative of the actual values at which the noncontrolling interests may ultimately be settled, which could vary significantly from the Company’s current estimates. The estimated fair values of noncontrolling interests subject to put provisions can fluctuate and the implicit multiple of earnings at which these noncontrolling interests obligations may be settled will vary significantly depending upon market conditions including potential purchasers’ access to the capital markets, which can impact the level of competition for dialysis and non-dialysis related businesses, the economic performance of these businesses and the restricted marketability of the third-party owners’ equity interests. The amount of noncontrolling interests subject to put provisions that employ a contractually predetermined multiple of earnings rather than fair value are immaterial.
Long-term incentive compensation	The Company’s stock-based compensation awards are measured at their estimated fair values on the date of grant if settled in shares or at their estimated fair values at the end of each reporting period if settled in cash. The value of stock-based awards so measured is recognized as compensation expense on a cumulative straight-line basis over the vesting terms of the awards, adjusted for expected forfeitures.
Comprehensive Income	Net realized losses on interest rate cap agreements that are reclassified into income are recorded as debt expense in the corresponding consolidated statements of operations. See Note 9 to these condensed consolidated financial statements for further details. Net realized gains on investment securities reclassified into income for the nine months ended September 30, 2017 were recognized in other income in the corresponding consolidated statements of operations. See Note 5 to these condensed consolidated financial statements for further details.
Variable Interest Entities	The Company relies on the operating activities of certain legal entities that it does not directly own or control, but over which it has indirect influence and of which it is considered the primary beneficiary. These entities are subject to the consolidation guidance applicable to variable interest entities (VIEs). Under U.S. generally accepted accounting principles (GAAP), VIEs typically include entities for which (i) the entity’s equity is not sufficient to finance its activities without additional subordinated financial support; (ii) the equity holders as a group lack the power to direct the activities that most significantly influence the entity’s economic performance, the obligation to absorb the entity’s expected losses, or the right to receive the entity’s expected returns; or (iii) the voting rights of some investors are not proportional to their obligations to absorb the entity’s losses. The Company has determined that substantially all of the legal entities it is associated with that qualify as VIEs must be included in its consolidated financial statements. A number of these VIEs are within the Company's DMG business, which is classified as held for sale and as a discontinued operation in these condensed consolidated financial statements. The Company manages these entities and provides operating and capital funding as necessary for these entities to accomplish their operational and strategic objectives. A number of these entities are subject to nominee share ownership or share transfer restriction agreements that effectively transfer the majority of the economic risks and rewards of their ownership to the Company. In other cases, the Company’s management agreements with these entities include both financial terms and protective and participating rights to the entities’ operating, strategic and non-clinical governance decisions which transfer substantial powers over and economic responsibility for the entities to the Company. In some cases, such entities are subject to broad exclusivity or noncompetition restrictions that benefit the Company. Further, in some cases, the Company has contractual arrangements with its related party nominee owners that effectively indemnify these parties from the economic losses from, or entitle the Company to the economic benefits of, these entities. The analyses upon which these consolidation determinations rest are complex, involve uncertainties, and require significant judgment on various matters, some of which could be subject to different interpretations.
Fair Value of Financial Instruments	Investments in mutual funds and common stock represent equity securities that are recorded at estimated fair value based upon quoted redemption prices reported by each mutual fund. See Note 5 to these condensed consolidated financial statements for further discussion. 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 9 to these condensed consolidated financial statements for further discussion. The estimated fair value of contingent earn-out obligations are primarily based on unobservable inputs including projected EBITDA. 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 credit risk-adjusted rate that is used to discount the obligations to present value.
New Accounting Standards	On May 28, 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. In 2015, 2016 and 2017, the FASB issued ASU 2015-14, ASU 2016-08, ASU 2016-10, ASU 2016-11, ASU 2016-12, and ASU 2017-10, each of which amends the guidance in ASU 2014-09. These ASUs replaced most existing revenue recognition guidance in GAAP. The Company adopted these ASUs beginning January 1, 2018. See Note 2 for further details. In January 2016, the FASB issued ASU No. 2016-01, Financial Instruments - Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities. In February 2018, the FASB issued ASU 2018-03, which provides various related technical corrections and improvements. The Company adopted these ASUs beginning January 1, 2018. See Note 5 for further details. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). The amendments in this ASU revise the accounting related to lessee accounting. Under the new guidance, lessees will be required to recognize a lease liability and a right-of-use asset for substantially all leases with lease terms in excess of twelve months. The new lease guidance also simplifies the accounting for sale and leaseback transactions primarily because lessees must recognize lease assets and lease liabilities. In July 2018, the FASB issued ASU No. 2018-10, Codification Amendments to Topic 842, and ASU No. 2018-11, which include targeted improvements to the guidance issued in ASU 2016-02. The amendments in these ASUs are effective for the Company beginning on January 1, 2019 and are to be applied through a modified retrospective transition approach for leases existing at, or entered into after, either at the beginning of the earliest comparative period presented in the financial statements or at the adoption date with a cumulative effect adjustment. Early adoption is permitted. The Company has assembled an internal cross-functional lease task force that meets regularly to discuss and evaluate the current lease portfolio and related systems, processes, controls and policy changes necessary. The Company has made progress in gathering the necessary data elements for the lease population and a system provider has been selected, with system configuration and implementation underway. The Company is currently evaluating the impact of the new guidance on its consolidated financial statements and believes it will have a material impact on its consolidated balance sheet but will not have a material impact on its results of operations or liquidity. The Company expects to adopt these ASUs by applying the new guidance on January 1, 2019 and recognizing a cumulative effect adjustment. The Company is currently planning on electing the package of practical expedients to not reassess prior conclusions related to contracts containing leases, lease classification and initial direct costs. The Company continues to evaluate other practical expedients available under the guidance as well as the effect that the implementation of this guidance will have on its consolidated financial statements, related disclosures and controls, and ongoing business policies and processes. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. The amendments in this ASU clarify how certain cash receipts and cash payments should be classified on the statement of cash flows. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted cash. The amendments in this ASU require that the statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. The adoption of these ASUs did not have a material impact on the Company’s consolidated financial statements when adopted on January 1, 2018. In October 2016, the FASB issued ASU No. 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory. The amendments in this ASU allow entities to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The current guidance does not allow recognition until the asset has been sold to an outside party. The amendments in this ASU are effective for the Company beginning on January 1, 2018 and are to be applied on a modified retrospective basis. The adoption of this ASU did not have a material impact on the Company’s consolidated financial statements when adopted on January 1, 2018. In August 2017, the FASB issued ASU No. 2017-12, Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities. The amendments in this ASU better align an entity’s risk management activities and financial reporting for hedging relationships through changes to both the designation and measurement guidance for qualifying hedging relationships and the presentation of hedge results. The amendments in the new ASU are effective for the Company on January 1, 2019 and are to be applied prospectively. The adoption of this ASU is not expected to have a material impact on the Company’s consolidated financial statements when adopted on January 1, 2019. In February 2018, the FASB issued ASU No. 2018-02, Income Statement - Reporting Comprehensive Income (Topic 220), Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which allows for the reclassification of certain income tax effects related to the 2017 Tax Act between “Accumulated other comprehensive income” and “Retained earnings.” This ASU relates to the requirement that adjustments to deferred tax liabilities and assets related to a change in tax laws or rates be included in “Income from continuing operations”, even in situations where the related items were originally recognized in “Other comprehensive income” (rather than in “Income from continuing operations”). The amendments in this ASU are effective for all entities for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years, with early adoption permitted. The Company elected to early adopt this ASU on January 1, 2018 and applied the change in the period of adoption. The adoption of this ASU resulted in the reclassification of an immaterial amount of deferred tax effects from accumulated other comprehensive income to retained earnings via a cumulative change in accounting principle effective January 1, 2018. See Note 14 for more details. 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 are effective for the Company beginning on January 1, 2020 and its new requirements are to be applied on a prospective basis. The adoption of this ASU is not expected to have a material impact on the Company’s consolidated financial statements.