Commitments and Contingencies - Available Lines of Credit, Outstanding Standby Letter of Credits, and Bonds (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Oct. 18, 2019
Line of Credit Facility [Line Items]
Multicurrency revolving line of credit			$ 500,000,000
Credit Facility [Member]
Line of Credit Facility [Line Items]
Multicurrency revolving line of credit	$ 500,000,000	$ 500,000,000
Long-term borrowings	0	0
Standby LOCs issued and outstanding	(64,948,000)	(41,072,000)
Line of credit facility, remaining borrowing capacity	235,052,000	258,928,000
Unsecured Multicurrency Revolving Lines of Credit [Member]
Line of Credit Facility [Line Items]
Multicurrency revolving line of credit	99,201,000	107,206,000
Standby LOCs issued and outstanding	(24,966,000)	(25,100,000)
Short-term borrowings	0	(173,000)
Line of credit facility, remaining borrowing capacity	74,235,000	81,933,000
Surety Bond [Member]
Line of Credit Facility [Line Items]
Unsecured surety bonds in force	162,912,000	136,004,000
Line of Credit [Member]
Line of Credit Facility [Line Items]
Long-term borrowings	0	0
Line of credit facility, remaining borrowing capacity	$ 435,052,000	$ 458,928,000