Credit Facility - Additional Information (Detail) - Unsecured Revolving Credit Facility [Member] - Credit Agreement [Member]		6 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Line of Credit Facility [Line Items]
Unsecured revolving credit facility available amount	$ 650,000,000	$ 650,000,000
Letters of credit sublimit under credit facility	100,000,000	100,000,000
Maximum amount of credit facility	$ 900,000,000	$ 900,000,000
Credit Agreement due date		Oct. 23, 2020
Interest on borrowings, description		Either (a) a Eurodollar Rate formula or (b) the Base Rate formula, each as set forth in the Credit Agreement.
Commitment fee percentage on undrawn balance	0.225%
Amounts drawn under credit facility	$ 0	$ 0
Maximum [Member]
Line of Credit Facility [Line Items]
Operating income leverage ratio		3.0
Minimum [Member]
Line of Credit Facility [Line Items]
Interest coverage ratio		3.0
Base Rate [Member]
Line of Credit Facility [Line Items]
Applicable margin for borrowing	0.50%
Eurodollar [Member]
Line of Credit Facility [Line Items]
Applicable margin for borrowing	1.50%