Long-Term Debt And Notes Payable (Components Of Debt) (Detail) - USD ($)	6 Months Ended		9 Months Ended	12 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2015	Dec. 31, 2016	Mar. 31, 2013	May 31, 2012
Debt Instrument [Line Items]
Long-term Commercial Paper			$ 500,000,000
Debt Instrument, Basis Spread on Variable Rate	5.00%
Net decrease in short-term debt	$ 0	$ 51,300,000
Long-term debt	$ 745,700,000			$ 745,300,000
number of days to maturity			397
Line of Credit Facility, Amended Maximum Borrowing Capacity					$ 500,000,000	$ 300,000,000
2.75% Notes Due 2018
Debt Instrument [Line Items]
Maturity Year Of Debt Instrument	2018
Debt Instrument, Interest Rate, Stated Percentage	2.75%			2.75%
Long-term debt	$ 249,400,000			$ 249,200,000
Debt Instrument, Face Amount	250,000,000			250,000,000
Amortization of Debt Issuance Costs	(600,000)			(800,000)
Six Point Five Five Percent Notes Due 2036 [Member]
Debt Instrument [Line Items]
Long-term debt	198,000,000			198,000,000
Debt Instrument, Face Amount	200,000,000			200,000,000
Amortization of Debt Issuance Costs	(1,300,000)			(1,300,000)
Debt Instrument, Unamortized Discount	(700,000)			(700,000)
Four Point Four Five Percent Notes Due 2023 [Member]
Debt Instrument [Line Items]
Long-term debt	298,300,000			298,100,000
Debt Instrument, Face Amount	300,000,000			300,000,000
Amortization of Debt Issuance Costs	$ (1,700,000)			$ (1,900,000)
4.45% Notes Due 2023
Debt Instrument [Line Items]
Maturity Year Of Debt Instrument	2023
Debt Instrument, Interest Rate, Stated Percentage	4.45%			4.45%
6.55% Notes Due 2036
Debt Instrument [Line Items]
Maturity Year Of Debt Instrument	2036
Debt Instrument, Interest Rate, Stated Percentage	6.55%			6.55%