Short-term Debt - 2018 Bank of America Credit Facility (Details) - USD ($)	1 Months Ended
	Apr. 30, 2018	Jun. 30, 2016	Mar. 31, 2020	Oct. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Oct. 31, 2018
Short-term Debt [Line Items]
Short-term debt			$ 33,158,000			$ 23,647,000
Bank of America | Bank of America 2018 Credit Agreement
Short-term Debt [Line Items]
Interest rate (as a percent)			3.63%			4.50%
Revolving Credit Facility And Other Financial Accommodations | Bank of America | Line of Credit | Bank of America 2018 Credit Agreement
Short-term Debt [Line Items]
Credit facility, maximum borrowing capacity	$ 250,000,000.0
Revolving Credit Facility | Bank of America | Line of Credit | Bank of America 2018 Credit Agreement
Short-term Debt [Line Items]
Credit facility, maximum borrowing capacity	$ 5,000,000.0			$ 15,000,000.0
Line of credit facility, expiration period	364 days
Short-term debt			$ 0			$ 1,100,000
Credit facility, remaining borrowing capacity			$ 243,600,000
Revolving Credit Facility | Bank of America | Standby Letters of Credit | Bank of America 2018 Credit Agreement
Short-term Debt [Line Items]
Credit facility, maximum borrowing capacity				6,400,000	$ 3,200,000
Line of credit facility, fair value of amount outstanding				$ 6,400,000			$ 3,200,000
Conversion Scenario One | Revolving Credit Facility | Bank of America | Line of Credit | Bank of America 2018 Credit Agreement
Short-term Debt [Line Items]
Credit facility, maximum borrowing capacity	$ 400,000,000.0
Credit facility, term		5 years
LIBOR | Revolving Credit Facility | Bank of America | Line of Credit | Bank of America 2018 Credit Agreement
Short-term Debt [Line Items]
Credit facility, basis spread on variable rate (as a percent)	2.75%
Minimum | LIBOR | Conversion Scenario One | Revolving Credit Facility | Bank of America | Line of Credit | Bank of America 2018 Credit Agreement
Short-term Debt [Line Items]
Credit facility, basis spread on variable rate (as a percent)	1.50%
Maximum | LIBOR | Conversion Scenario One | Revolving Credit Facility | Bank of America | Line of Credit | Bank of America 2018 Credit Agreement
Short-term Debt [Line Items]
Credit facility, basis spread on variable rate (as a percent)	2.00%