Fair value measurements - Assets and Liabilities on Recurring and Nonrecurring Basis (Details) $ in Thousands	9 Months Ended
Sep. 30, 2021 USD ($) transfer	Dec. 31, 2020 USD ($)
Assets and liabilities measured at fair value
Transfers in Fair Value Hierarchy \| transfer	0
Investments	$ 2,046,878	$ 1,611,114
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Secured notes payable	198,758	230,925
Unsecured senior notes payable	8,314,851	7,232,370
Unsecured senior lines of credit	749,978	99,991
Commercial Paper
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Commercial Paper Program	749,978
Book value
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Secured notes payable	198,758	230,925
Unsecured senior notes payable	8,314,851	7,232,370
Book value \| Commercial Paper
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Commercial Paper Program	749,978	99,991
Book value \| Unsecured senior line of credit
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Unsecured senior lines of credit	0	0
Fair Value \| Fair value measured on nonrecurring basis
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Secured notes payable, fair value	208,553	249,782
Unsecured senior notes payable, fair value	9,031,303	8,447,845
Fair Value \| Fair value measured on nonrecurring basis \| Commercial Paper
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Commercial paper, fair value disclosure	749,986	99,998
Fair Value \| Fair value measured on nonrecurring basis \| Unsecured senior line of credit
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Unsecured senior lines of credit, fair value	0	0
Fair Value \| Fair value measured on nonrecurring basis \| Quoted prices in active markets for identical assets (Level 1) \| Commercial Paper
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Commercial paper, fair value disclosure	0	0
Fair Value \| Fair value measured on nonrecurring basis \| Quoted prices in active markets for identical assets (Level 1) \| Unsecured senior line of credit
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Unsecured senior lines of credit, fair value	0	0
Fair Value \| Fair value measured on nonrecurring basis \| Significant other observable inputs (Level 2)
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Secured notes payable, fair value	208,553	249,782
Unsecured senior notes payable, fair value	9,031,303	8,447,845
Fair Value \| Fair value measured on nonrecurring basis \| Significant other observable inputs (Level 2) \| Commercial Paper
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Commercial paper, fair value disclosure	749,986	99,998
Fair Value \| Fair value measured on nonrecurring basis \| Significant other observable inputs (Level 2) \| Unsecured senior line of credit
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Unsecured senior lines of credit, fair value	0	0
Fair Value \| Fair value measured on nonrecurring basis \| Significant unobservable input (Level 3) \| Commercial Paper
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Commercial paper, fair value disclosure	0	0
Fair Value \| Fair value measured on nonrecurring basis \| Significant unobservable input (Level 3) \| Unsecured senior line of credit
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Unsecured senior lines of credit, fair value	0	0
Investments in publicly traded companies
Assets and liabilities measured at fair value
Investments at fair value	657,331	559,830
Investments in publicly traded companies \| Fair Value \| Fair value measured on recurring basis
Assets and liabilities measured at fair value
Investments at fair value	657,331	559,830
Investments in publicly traded companies \| Fair Value \| Fair value measured on recurring basis \| Quoted prices in active markets for identical assets (Level 1)
Assets and liabilities measured at fair value
Investments at fair value	657,331	559,830
Investments in publicly traded companies \| Fair Value \| Fair value measured on recurring basis \| Significant other observable inputs (Level 2)
Assets and liabilities measured at fair value
Investments at fair value	0	0
Investments in publicly traded companies \| Fair Value \| Fair value measured on recurring basis \| Significant unobservable input (Level 3)
Assets and liabilities measured at fair value
Investments at fair value	0	0
Investments in privately held entities that report NAV
Assets and liabilities measured at fair value
Investments at fair value	835,812	662,082
Entities without observable price changes \| Investments in privately held entities that do not report NAV
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Investments in privately held entities that do not report fair value, book value	349,100	244,798
Entities without observable price changes \| Investments in privately held entities that do not report NAV \| Fair Value \| Fair value measured on nonrecurring basis
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Investments in privately held entities that do not report fair value, book value	135,524	157,871
Entities without observable price changes \| Investments in privately held entities that do not report NAV \| Fair Value \| Fair value measured on nonrecurring basis \| Quoted prices in active markets for identical assets (Level 1)
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Investments in privately held entities that do not report fair value, book value	0	0
Entities without observable price changes \| Investments in privately held entities that do not report NAV \| Fair Value \| Fair value measured on nonrecurring basis \| Significant other observable inputs (Level 2)
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Investments in privately held entities that do not report fair value, book value	129,468	144,404
Entities without observable price changes \| Investments in privately held entities that do not report NAV \| Fair Value \| Fair value measured on nonrecurring basis \| Significant unobservable input (Level 3)
Fair Value Measurements, Nonrecurring Value Measurement [Abstract]
Investments in privately held entities that do not report fair value, book value	$ 6,056	$ 13,467

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Including the current and noncurrent portions, fair value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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Transfers in Fair Value Hierarchy

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Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as current.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI) and investment in equity security without readily determinable fair value.

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Amount of investment in equity security without readily determinable fair value.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Fair value portion of contractual arrangement with a lender under which borrowings can be made up to a specific amount at any point in time.

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Fair value portion of notes payable.

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Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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Carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders.

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