Derivative Instruments - Additional Information (Detail) (USD $)	0 Months Ended	1 Months Ended	9 Months Ended		1 Months Ended			0 Months Ended			1 Months Ended
	Sep. 29, 2011	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2011 Interest Rate Exchange Agreement Expiring 2010	Dec. 31, 2010 Interest Rate Exchange Agreement Expiring 2010	Apr. 15, 2010 Interest Rate Exchange Agreement Expiring 2010	Jul. 12, 2012 Interest Rate Exchange Agreement Expiring 2011	Sep. 29, 2011 Interest Rate Exchange Agreement Expiring 2011	Jul. 12, 2011 Interest Rate Exchange Agreement Expiring 2011	Dec. 31, 2011 Interest Rate Exchange Agreements Expiring 2011 And 2012	Dec. 31, 2010 4.5% Senior Notes, due December 2020	Dec. 06, 2010 4.5% Senior Notes, due December 2020	Apr. 15, 2010 4.5% Senior Notes, due December 2020	Dec. 09, 2011 4.2% Senior Notes, due December 2021
Derivative [Line Items]
Notional amount	$ 350,000,000.0						$ 300,000,000.0			$ 350,000,000.0
Interest rate on senior notes												4.50%	4.50%	4.50%	4.20%
Interest rate contract settlement amount						31,000,000			34,700,000
Amortization of interest expense			1,275,000	1,109,000		31,000,000					37,900,000
Term of amortized interest expense, years					10 years	10 years
Interest rate						5.80%					5.30%
Interest rate exchange agreement expiration date	Feb. 28, 2012							Sep. 30, 2011
Additional interest rate contract settlement		4,000,000
Settlement amount interest rate contract											38,700,000
Interest rate settlement recognized as other expense											800,000
Amount to be recognized from hedged transactions within 12 months, approximate			$ 7,300,000