Long-Term Debt - Additional Information (Detail) (USD $)	9 Months Ended	0 Months Ended	8 Months Ended			8 Months Ended		12 Months Ended
	Sep. 30, 2014	Feb. 07, 2014 Revolving Credit Facility	Sep. 30, 2014 Revolving Credit Facility	Feb. 07, 2014 Revolving Credit Facility	Sep. 22, 2011 Revolving Credit Facility	Sep. 30, 2014 Revolving Credit Facility Minimum	Sep. 30, 2014 Revolving Credit Facility Maximum	Dec. 31, 2005 5.10% Senior Notes	Jan. 20, 2005 5.10% Senior Notes
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 750,000,000.0	$ 750,000,000.0
Additional borrowing capacity				250,000,000.0
Interest rate margin			1.00%			0.90%	1.50%
Commercial paper classified as current	355,876,000
Weighted average interest rate	0.31%
Weighted average maturity period	20 days	5 years
Principal amount									$ 325,000,000.0
Maturity date								Feb. 01, 2015