Summary of Significant Accounting Policies - Fair Value Measurements (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Assets and liabilities carried at fair value measured on a recurring basis
Money Market Funds	$ 0	$ 585,000,000
Time Deposits		24,482,000
Fair Value, Measurements, Recurring \| Quoted prices in active markets (Level 1)
Assets and liabilities carried at fair value measured on a recurring basis
Money Market Funds		0
Time Deposits	0	0
Trading Securities	10,248,000	11,279,000
Derivative Assets	0	0
Derivative Liabilities		0
Interest Rate Swap Agreements Liabilities	0
Fair Value, Measurements, Recurring \| Significant other observable inputs (Level 2)
Assets and liabilities carried at fair value measured on a recurring basis
Money Market Funds		585,000,000
Time Deposits	956,000	24,482,000
Trading Securities	505,000	505,000
Derivative Assets	93,000	1,579,000
Derivative Liabilities		2,329,000
Interest Rate Swap Agreements Liabilities	973,000
Fair Value, Measurements, Recurring \| Significant unobservable inputs (Level 3)
Assets and liabilities carried at fair value measured on a recurring basis
Money Market Funds		0
Time Deposits	0	0
Trading Securities	0	0
Derivative Assets	0	0
Derivative Liabilities		0
Interest Rate Swap Agreements Liabilities	0
Fair Value, Measurements, Recurring \| Estimated Fair Value
Assets and liabilities carried at fair value measured on a recurring basis
Money Market Funds		585,000,000
Time Deposits	956,000	24,482,000
Trading Securities	10,753,000	11,784,000
Derivative Assets	93,000	1,579,000
Derivative Liabilities		$ 2,329,000
Interest Rate Swap Agreements Liabilities	$ 973,000

Fair value of all liability derivatives designated as cash flow hedging instruments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

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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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Fair value portion of asset contracts related to the exchange of different currencies, including, but not limited to, foreign currency options, forward contracts, and swaps.

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Fair value portion of liability contracts related to the exchange of different currencies, including, but not limited to, foreign currency options, forward (delivery or nondelivery) contracts, and swaps entered into.

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Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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Any certificate of deposit or savings account held by a bank or other financial institution for a short-term specified period of time. Because of their short-term, time deposits are considered highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading) and investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
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