Debt - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Mar. 26, 2021	Jul. 10, 2020	Jun. 30, 2020
Debt Instrument [Line Items]
Long-term debt	$ 694,300,000		$ 694,300,000				$ 551,800,000
Letters of credit issued	5,400,000		5,400,000
Short-term credit agreement borrowings	0		0				170,000,000.0
Interest costs	10,100,000	$ 7,200,000	30,400,000	$ 22,100,000
Interest costs, capitalized	1,200,000	2,300,000	6,900,000	6,500,000
Debt extinguishment losses, net	0	$ 0	8,200,000	$ (0.0)
Interest Rate Swaps
Debt Instrument [Line Items]
Derivative, gain on derivative			$ 2,300,000
Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Current borrowing capacity					$ 300,000,000.0
Debt instrument, covenant, credit commitment amount					300,000,000.0
Maximum borrowing capacity					500,000,000.0
Commitment fee rate			0.35%
Short-term credit agreement borrowings	0		$ 0
Credit Agreement available for future borrowings	$ 294,600,000		$ 294,600,000
Borrowing rate	2.11%		2.11%
Required interest coverage ratio one			3.00
Required interest coverage ratio two			3.50
Minimum available liquidity	$ 150,000,000.0		$ 150,000,000.0
Asset coverage ratio			1.10
Line of Credit | Letters of credit
Debt Instrument [Line Items]
Maximum borrowing capacity					$ 40,000,000.0
Letter of credit fees			2.00%
Minimum | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Commitment fee rate			0.275%
Minimum | Line of Credit | Letters of credit
Debt Instrument [Line Items]
Letter of credit fees			1.25%
Maximum | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Commitment fee rate			0.375%
Required debt to capital ratio (less than)	0.55		0.55
Maximum | Line of Credit | Letters of credit
Debt Instrument [Line Items]
Letter of credit fees			2.25%
LIBOR | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Interest rate margin			2.00%
LIBOR | Minimum | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Interest rate margin			1.25%
LIBOR | Maximum | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Interest rate margin			2.25%
Base Rate | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Interest rate margin			1.00%
Base Rate | Minimum | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Interest rate margin			0.25%
Base Rate | Maximum | Line of Credit | Revolving Credit Facility
Debt Instrument [Line Items]
Interest rate margin			1.25%
Senior unsecured notes, 6.375% due July 2028
Debt Instrument [Line Items]
Face amount	$ 400,000,000.0		$ 400,000,000.0			$ 400,000,000
Interest rate	6.375%		6.375%			6.375%
Long-term debt	$ 394,900,000		$ 394,900,000				0
Senior unsecured notes, 5.20% due July 2021
Debt Instrument [Line Items]
Face amount						$ 250,000,000.0	$ 250,000,000.0
Interest rate							5.20%
Long-term debt	0		0				$ 252,300,000
Debt extinguishment losses, net			10,500,000
Senior unsecured notes, 4.45% due March 2023
Debt Instrument [Line Items]
Face amount	$ 300,000,000.0		$ 300,000,000.0				$ 300,000,000.0
Interest rate	4.45%		4.45%		4.45%		4.45%
Long-term debt	$ 299,400,000		$ 299,400,000		$ 300,000,000.0		$ 299,500,000