Debt - Narrative (Details) - USD ($)	3 Months Ended		6 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Jun. 30, 2021	Mar. 26, 2021	Jul. 10, 2020
Debt Instrument [Line Items]
Long-term debt	$ 695,000,000.0		$ 695,000,000.0		$ 694,500,000
Letters of credit issued	5,300,000		5,300,000
Interest costs	10,300,000	$ 10,900,000	20,600,000	$ 20,300,000
Interest costs, capitalized	200,000	3,000,000	300,000	5,700,000
Debt prepayment costs	0	0	$ 0	(8,200,000)
Fair value hedging
Debt Instrument [Line Items]
Derivative, gain on derivative				2,300,000
Interest Rate Swaps | Fair value hedging
Debt Instrument [Line Items]
Derivative, gain on derivative				2,300,000
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
Credit Agreement available for future borrowings	$ 294,700,000		$ 294,700,000
Borrowing rate	2.10%		2.10%
Required interest coverage ratio one			3.00
Required interest coverage ratio two			3.50
Minimum available liquidity	$ 150,000,000		$ 150,000,000
Asset coverage ratio			1.10
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%
Required debt to capital ratio (less than)	0.55		0.55
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, 6.375% due July 2028
Debt Instrument [Line Items]
Face amount	$ 400,000,000		$ 400,000,000		$ 400,000,000		$ 400,000,000
Interest rate	6.375%		6.375%		6.375%		6.375%
Long-term debt	$ 395,400,000		$ 395,400,000		$ 395,000,000.0
Senior unsecured notes, 5.20% due July 2021
Debt Instrument [Line Items]
Face amount							$ 250,000,000
Debt prepayment costs	0	$ 0	0	$ 10,500,000
Senior unsecured notes, 4.45% due March 2023
Debt Instrument [Line Items]
Face amount	$ 300,000,000		$ 300,000,000		$ 300,000,000
Interest rate	4.45%		4.45%		4.45%	4.45%
Long-term debt	$ 299,600,000		$ 299,600,000		$ 299,500,000	$ 300,000,000