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Long-term Debt (Schedule Of Long-Term Debt) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Debt Instrument [Line Items]
Long-term debt and capital lease obligation	$ 818,477	$ 602,900
4.10% Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt and capital lease obligation	$ 347,530	347,091
Senior notes, interest rate	4.10%
Debt instruments maturity date	2022
3.78% Senior Notes [Member]
Debt Instrument [Line Items]
Long-term debt and capital lease obligation	$ 250,000	250,000
Senior notes, interest rate	3.78%		3.78%
Debt instruments maturity date	2029
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long-term debt and capital lease obligation	$ 215,619	0
Capital Lease Obligation [Member]
Debt Instrument [Line Items]
Long-term debt and capital lease obligation	$ 5,328	$ 5,809

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- Definition

Debt instruments maturity date.

+ References

No definition available.

+ Details

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X

- Definition

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

+ References

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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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

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- Definition

Amount of long-term debt and capital lease obligation due after one year or beyond the normal operating cycle, if longer.

+ References

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(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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