Borrowing Facilities (Narrative) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019	Jul. 20, 2018
Credit Agreement [Member]
Line of Credit Facility [Line Items]
Credit Agreement capacity	$ 650,000
Description of variable interest rate basis	Interest on outstanding borrowings under the Credit Agreement (other than swingline loans) accrues, at the Company’s option, at (a) the London Interbank Offered Rate (LIBOR) plus 1.0% to 2.0% or (b) the base rate plus 0.0% to 1.0%.
Credit Agreement covenant terms	The Credit Agreement contains certain financial covenants as to interest coverage and debt leverage, and certain customary affirmative and negative covenants, including restrictions on the Company’s ability to incur additional debt and liens, pay dividends, repurchase shares, sell assets and merge or consolidate with other persons. Amounts due under the Credit Agreement could be accelerated upon specified events of default, including a failure to pay amounts due, breach of a covenant, material inaccuracy of a representation, or occurrence of bankruptcy or insolvency, subject, in some cases, to cure periods.
Credit agreement, secured by percentage of stock of the Company's domestic subsidiaries	100.00%
Credit agreement, secured by percentage of voting capital stock of each direct foreign subsidiary	65.00%
Credit Agreement [Member] | Bank Of America Credit Agreement [Member]
Line of Credit Facility [Line Items]
Credit Agreement description	On July 20, 2018, the Company entered into a $650 million credit agreement (the Credit Agreement) by and among the Company, certain of its subsidiaries, the lenders party thereto and Bank of America, N.A.,as Administrative Agent, Swingline Lender and a L/C Issuer. The Credit Agreement is comprised of a 5-year $500 million revolving credit facility (the Revolving Credit Facility) and a 5-year $150 million term loan facility (the Term Loan Facility), both with a maturity date of July 20, 2023. The Term Loan Facility proceeds were used to (i) refinance a portion of existing indebtedness and terminate all commitments under the Company’s prior $430 million credit agreement and (ii) pay the fees, costs and expenses associated with the foregoing and the negotiation, execution and delivery of the Credit Agreement. The Revolving Credit Facility is available for general corporate purposes. The Credit Agreement includes an accordion feature pursuant to which the Company is permitted to add one or more incremental term loan and/or increase commitments under the Revolving Credit Facility in an aggregate amount not exceeding $275 million, subject to the satisfaction of certain conditions.
Credit Agreement issuer	Bank of America, N.A.,
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit Agreement capacity	$ 500,000
Term period	5 years
Credit Agreement maturity date	Jul. 20, 2023
Possible increase to total commitments under Credit Agreement	$ 275,000
Principal amount	15,000	$ 0
Letters of credit outstanding amount	3,700
Revolving credit facility, available for future borrowings	$ 481,300		$ 430,000
Term Loan Facility [Member]
Line of Credit Facility [Line Items]
Term period	5 years
Credit Agreement maturity date	Jul. 20, 2023
Term Loan proceeds			$ 150,000
Term Loan frequency of periodic payments	quarterly
Derivative Notional Amount	$ 138,800
Principal amount	$ 138,750	$ 144,375
Debt Instrument, Interest Rate, Stated Percentage	2.928%
Term Loan Facility [Member] | Interest Rate Swap [Member]
Line of Credit Facility [Line Items]
Derivative Notional Amount	$ 138,800
Term Loan Facility [Member] | Bank Of America Credit Agreement [Member]
Line of Credit Facility [Line Items]
Quarterly principal installments	$ 1,900
Minimum [Member] | Credit Agreement [Member]
Line of Credit Facility [Line Items]
U.S. Credit facility, commitment fee	0.20%
Maximum [Member] | Credit Agreement [Member]
Line of Credit Facility [Line Items]
U.S. Credit facility, commitment fee	0.30%
LIBOR Plus [Member] | Minimum [Member] | Credit Agreement [Member]
Line of Credit Facility [Line Items]
U.S. Credit facility, commitment fee	1.00%
LIBOR Plus [Member] | Maximum [Member] | Credit Agreement [Member]
Line of Credit Facility [Line Items]
U.S. Credit facility, commitment fee	2.00%
Alternate Base Rate Plus [Member] | Minimum [Member] | Credit Agreement [Member]
Line of Credit Facility [Line Items]
U.S. Credit facility, commitment fee	0.00%
Alternate Base Rate Plus [Member] | Maximum [Member] | Credit Agreement [Member]
Line of Credit Facility [Line Items]
U.S. Credit facility, commitment fee	1.00%