Short-Term Borrowings (Details)	6 Months Ended
	Jun. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Short-term Debt [Line Items]
Line of Credit Facility, Commitment Fee Percentage	0.35%
Short-term Debt, Maximum Amount Outstanding During Period	$ 350,000,000.0
Ratio of Indebtedness to Net Capital	0.65
Notional Amount of Nonderivative Instruments	$ 100,000,000.0
Number of short-term lines of Credit, rate swap	3
Line of Credit Facility, Maximum Borrowing Capacity	$ 465,000,000
Line of Credit, Current	284,913,000	$ 244,190,000
Line of Credit Facility, Remaining Borrowing Capacity	180,087,000
Line of Credit Facility, Maximum Borrowing Capacity, Incremental	95,000,000.0
Line of Credit, Current, Incremental	0	0
Line of Credit Facility, Remaining Borrowing Capacity, Incremental	95,000,000
Line of Credit Facility, Maximum Borrowing Capacity, Existing	370,000,000
Line of Credit, Current, Existing	284,913,000	244,190,000
Line of Credit Facility, Remaining Borrowing Capacity, Existing	85,087,000
Bank Overdrafts	1,492,000	3,181,000
Short-term borrowing	$ 286,405,000	$ 247,371,000
Short-term Debt, Weighted Average Interest Rate, at Point in Time	1.05%	2.62%
Number Of Unsecured Bank Credit Facilities	4
Number Of Financial Institutions With Bank Credit Facilities	4
Line Of Credit Facility Maximum Borrowing Committed Capacity	$ 220,000,000.0
ParticipatingLendersInTheRevolver	5
Committed Line of Credit Facility Two [Member]
Short-term Debt [Line Items]
Debt Instrument, Description of Variable Rate Basis	LIBOR rate, plus 0.75 percent
Line of Credit Facility, Maximum Borrowing Capacity	$ 80,000,000
Line of Credit, Current	77,501,000	$ 57,150,000
Line of Credit Facility, Remaining Borrowing Capacity	$ 2,499,000
Committed Line of Credit Facility Three [Member]
Short-term Debt [Line Items]
Debt Instrument, Description of Variable Rate Basis	Lender's base rate, plus 0.75 percent
Line of Credit Facility, Maximum Borrowing Capacity	$ 45,000,000
Line of Credit, Current	32,412,000	42,040,000
Line of Credit Facility, Remaining Borrowing Capacity	$ 12,588,000
Committed Line of Credit Facility Five [Member]
Short-term Debt [Line Items]
Debt Instrument, Description of Variable Rate Basis	Lender's base rate, plus 0.85 percent
Line of Credit Facility, Maximum Borrowing Capacity	$ 40,000,000
Line of Credit, Current	40,000,000	40,000,000
Line of Credit Facility, Remaining Borrowing Capacity	$ 0
Committed Line of Credit Facility Four [Member]
Short-term Debt [Line Items]
Debt Instrument, Description of Variable Rate Basis	LIBOR rate, plus 1.125 percent
Line of Credit Facility, Maximum Borrowing Capacity	$ 150,000,000.0
Line of Credit, Current	80,000,000	50,000,000
Line of Credit Facility, Remaining Borrowing Capacity	$ 70,000,000
Committed Line of Credit Facility Six [Member]
Short-term Debt [Line Items]
Debt Instrument, Description of Variable Rate Basis	LIBOR rate, plus 1.75 percent
Line of Credit Facility, Maximum Borrowing Capacity	$ 35,000,000
Line of Credit Facility, Remaining Borrowing Capacity	$ 35,000,000
Committed Line of Credit Facility Seven [Member]
Short-term Debt [Line Items]
Debt Instrument, Description of Variable Rate Basis	LIBOR rate, plus 1.75 percent
Line of Credit Facility, Maximum Borrowing Capacity	$ 15,000,000
Line of Credit Facility, Remaining Borrowing Capacity	$ 15,000,000
Committed Line of Credit Facility Eight [Member]
Short-term Debt [Line Items]
Debt Instrument, Description of Variable Rate Basis	LIBOR rate, plus 1.75 percent
Line of Credit Facility, Maximum Borrowing Capacity	$ 25,000,000
Line of Credit Facility, Remaining Borrowing Capacity	$ 25,000,000
Committed Line of Credit Facility Nine [Member]
Short-term Debt [Line Items]
Debt Instrument, Description of Variable Rate Basis	LIBOR rate, plus 1.75 percent
Debt Instrument, Description of Variable Rate Basis	1.75%
Line of Credit Facility, Maximum Borrowing Capacity	$ 20,000,000
Line of Credit Facility, Remaining Borrowing Capacity	$ 20,000,000
Interest Rate Swap Rate, Low Range [Member]
Short-term Debt [Line Items]
Fixed Swap Rate	26.15%
Interest Rate Swap Rate, High Range [Member]
Short-term Debt [Line Items]
Fixed Swap Rate	38.75%
Committed Line of Credit Facility One [Member]
Short-term Debt [Line Items]
Debt Instrument, Description of Variable Rate Basis	LIBOR rate, plus 0.75 percent
Line of Credit Facility, Maximum Borrowing Capacity	$ 55,000,000
Line of Credit, Current	55,000,000	$ 55,000,000
Line of Credit Facility, Remaining Borrowing Capacity	$ 0