Derivative Instruments - Additional Information (Detail) (USD $)	1 Months Ended		12 Months Ended			1 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2010	Apr. 30, 2010	Oct. 31, 2011	Jul. 31, 2011	Sep. 29, 2011	Apr. 15, 2010	Jul. 12, 2011	Dec. 06, 2010
Derivative [Line Items]
Interest rate contract with notional amount										$ 350,000,000
Interest rate exchange agreement expiration date		Feb. 28, 2012
Future amortization interest expense over 10 year periods			1,723,000	1,703,000	1,685,000
Additional interest rate contract settlement	4,000,000
Amount to be recognized from hedged transactions within 12 months, approximate			(7,000,000)
Interest Rate Exchange Agreement Expiring 2010
Derivative [Line Items]
Interest rate contract with notional amount											300,000,000
Interest rate exchange agreement expiration date							Dec. 31, 2010
Interest rate contract settlement amount						31,000,000
Future amortization interest expense over 10 year periods						31,000,000
Term of amortized interest expense, years						10 years
Interest rate					5.80%
Interest Rate Exchange Agreement Expiring 2011
Derivative [Line Items]
Interest rate contract with notional amount												350,000,000
Interest rate exchange agreement expiration date									Sep. 30, 2011
Interest rate contract settlement amount								34,700,000
Interest Rate Exchange Agreements Expiring 2011 And 2012
Derivative [Line Items]
Future amortization interest expense over 10 year periods	37,900,000
Interest rate				5.30%
Settlement amount interest rate contract				38,700,000
Interest rate settlement recognized as other expense	$ 800,000
4.5 % Senior Notes
Derivative [Line Items]
Interest rate on senior notes											4.50%		4.50%