Debt - Narrative (Details)	3 Months Ended				6 Months Ended
	Sep. 30, 2022 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2022 USD ($) Rate	Sep. 30, 2021 USD ($)	Dec. 31, 2022	Jun. 30, 2022 USD ($)	Apr. 30, 2022 USD ($)	Mar. 16, 2022 USD ($)	Mar. 26, 2021 USD ($)
Debt Instrument [Line Items]
Long-term debt	$ 692,100,000	$ 692,100,000	$ 692,100,000			$ 691,800,000
Letters of credit issued	1,800,000	$ 1,800,000	1,800,000
Interest costs	12,900,000			$ 10,300,000
Interest costs, capitalized	300,000			$ 100,000
Line of Credit | Maximum
Debt Instrument [Line Items]
Required debt to capital ratio (less than)						0.55
Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Current borrowing capacity									$ 300,000,000
Debt instrument, covenant, credit commitment amount									300,000,000
Maximum borrowing capacity									500,000,000
Commitment fee rate		0.35%
Short-term credit agreement borrowings	0	$ 0	0
Credit Agreement available for future borrowings	$ 298,200,000	$ 298,200,000	$ 298,200,000
Borrowing rate	5.12%	5.12%	5.12%
Required interest coverage ratio one			200.00%			2.00
Required interest coverage ratio two		3.00	300.00%
Asset coverage ratio | Rate			110.00%
Revolving Credit Facility | Line of Credit | Forecast
Debt Instrument [Line Items]
Required interest coverage ratio two					3.50
Revolving Credit Facility | Line of Credit | LIBOR
Debt Instrument [Line Items]
Interest rate margin		2.00%
Revolving Credit Facility | Line of Credit | Base Rate
Debt Instrument [Line Items]
Interest rate margin		1.00%
Revolving Credit Facility | Line of Credit | Minimum
Debt Instrument [Line Items]
Commitment fee rate		0.275%
Revolving Credit Facility | Line of Credit | Minimum | LIBOR
Debt Instrument [Line Items]
Interest rate margin		1.25%
Revolving Credit Facility | Line of Credit | Minimum | Base Rate
Debt Instrument [Line Items]
Interest rate margin		0.25%
Revolving Credit Facility | Line of Credit | Maximum
Debt Instrument [Line Items]
Commitment fee rate		0.375%
Revolving Credit Facility | Line of Credit | Maximum | LIBOR
Debt Instrument [Line Items]
Interest rate margin		2.25%
Revolving Credit Facility | Line of Credit | Maximum | Base Rate
Debt Instrument [Line Items]
Interest rate margin		1.25%
Letters of credit | Line of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity									$ 40,000,000
Letter of credit fees		2.00%
Letters of credit | Line of Credit | Minimum
Debt Instrument [Line Items]
Letter of credit fees		1.25%
Letters of credit | Line of Credit | Maximum
Debt Instrument [Line Items]
Letter of credit fees		2.25%
Senior unsecured notes, 7.625% due March 2030
Debt Instrument [Line Items]
Face amount	$ 300,000,000	$ 300,000,000	$ 300,000,000			$ 300,000,000		$ 300,000,000
Interest rate	7.625%	7.625%	7.625%			7.625%		7.625%
Long-term debt	$ 296,100,000	$ 296,100,000	$ 296,100,000			$ 295,900,000
Senior unsecured notes, 4.45% due March 2023
Debt Instrument [Line Items]
Face amount							$ 300,000,000
Interest rate							4.45%		4.45%
Long-term debt									$ 300,000,000