Debt - Notes - Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Unsecured notes	$ 5,534,990	$ 5,038,812
Debt instrument, maturity date	Jan. 10, 2022
3.50% Notes [Member]
Debt Instrument [Line Items]
Proceeds from issuance of unsecured debt	$ 500,000
Debt instrument, interest rate, stated percentage	3.50%
Proceeds from debt, net of issuance costs	$ 497,000
Debt instrument, interest rate, effective percentage	3.61%
Notes Payable, Other Payables [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date	Aug. 01, 2047
Weighted average interest rate	4.25%
Notes Payable, Other Payables [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	2.375%
Notes Payable, Other Payables [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	7.57%

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (a)
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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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- Definition

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.

+ References

No definition available.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
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- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

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- Definition

Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

+ References

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- Definition

The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

+ References

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-Publisher FASB
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- Definition

The cash inflow from the issuance of long-term debt that is not secured by collateral. Excludes proceeds from tax exempt unsecured debt.

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