Short-Term and Long-Term Debt, Including Finance Leases - Credit Facility (Narrative) (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) quarter	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Debt instrument, interest period	1 month
Line of credit facility, collateral, capital stock, percent	100.00%
Number of quarters | quarter	4
Short-term borrowings	$ 28,531,000	$ 23,195,000
Interest expense, debt	11,519,000	11,399,000	$ 9,909,000
Interest paid	$ 10,470,000	10,381,000	$ 8,394,000
Minimum
Debt Instrument [Line Items]
Lessee leasing arrangements, finance leases, term of contract	24 months
Maximum
Debt Instrument [Line Items]
Lessee leasing arrangements, finance leases, term of contract	60 months
Credit Facility
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	$ 450,000,000
Credit facility	176,877,000	190,316,000
Line of credit facility, remaining borrowing capacity	265,264,000
Short-term borrowings	$ 28,531,000	$ 23,195,000
Credit Facility | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate (percent)	1.00%
Credit Facility | Minimum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate (percent)	1.30%
Credit Facility | Minimum | Base Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate (percent)	0.30%
Credit Facility | Maximum | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate (percent)	2.10%
Credit Facility | Maximum | Base Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate (percent)	1.10%
Credit Facility | UK Borrower
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	$ 185,000,000
Credit Facility | Canadian Borrower
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	75,000,000
Credit Facility | Australian Borrower
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	$ 32,500,000
Credit Facility | Wells Fargo Bank, National Association | 2015 Amendment to Credit Agreement
Debt Instrument [Line Items]
Debt instrument, covenant, coverage ratio	1.10
Debt instrument, maximum senior secured leverage ratio	3.25
Debt instrument, maximum total leverage ratio	4.25
Letter of credit subcommitment
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	$ 100,000,000
Line of credit facility, remaining borrowing capacity	$ 11,636,000
Base Rate Loans | Credit Facility | Federal Funds Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate (percent)	0.50%