Bank Debt (Narrative) (Details)	3 Months Ended
Mar. 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Revolving credit facility	$ 350,000,000
Maturity date of bank borrowings	Mar. 28, 2022
Maximum borrowing capacity	$ 450,000,000
Aggregate bank borrowings	0
Additional bank borrowings	$ 347,000,000
LIBOR [Member]
Line of Credit Facility [Line Items]
Debt facility, applicable margin	1.00%
LIBOR [Member] \| Minimum [Member]
Line of Credit Facility [Line Items]
Debt facility, applicable margin	1.00%
LIBOR [Member] \| Maximum [Member]
Line of Credit Facility [Line Items]
Debt facility, applicable margin	2.00%
Base Rate [Member]
Line of Credit Facility [Line Items]
Debt facility, applicable margin	0.00%
Base Rate [Member] \| Minimum [Member]
Line of Credit Facility [Line Items]
Debt facility, applicable margin	0.00%
Base Rate [Member] \| Maximum [Member]
Line of Credit Facility [Line Items]
Debt facility, applicable margin	1.00%
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Additional bank borrowings	$ 3,000,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Consolidated leverage ratio	350.00%
Consolidated interest coverage ratio	6350.00%
Consolidated leverage ratio	0.00%
Revolving Credit Facility [Member] \| Minimum [Member]
Line of Credit Facility [Line Items]
Consolidated interest coverage ratio	200.00%

Debt instrument, consolidated fixed charge coverage ratio.

No definition available.

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Period Type:	duration

- Definition

Debt instrument, consolidated leverage ratio.

+ References

No definition available.

+ Details

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- Definition

Debt instrument, maximum consolidated leverage ratio in effect first quarter of each calendar year.

+ References

No definition available.

+ Details

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

+ Details

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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.

+ Details

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the noncurrent portion 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.

+ 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

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 45
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=99376301&loc=d3e1336-112600

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 45
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=99376301&loc=d3e1314-112600

+ Details

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Namespace Prefix:	us-gaap_
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- Details

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- Details

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- Details

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