Derivative Instruments (Additional Information) (Detail) $ in Thousands	6 Months Ended		24 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Dec. 31, 2011 USD ($) instrument
Derivative [Line Items]
Amortization of interest expense	$ 860	$ 859
Amount to be recognized from hedged transactions within 12 months, approximate	$ 6,900
Interest Rate Exchange Agreement Expiring 2010 and 2011
Derivative [Line Items]
Amortization of interest expense			$ 68,900
Term of amortized interest expense, years			10 years
4.5% Senior Notes, due December 2020
Derivative [Line Items]
Interest rate on senior notes			4.50%
4.2% Senior Notes, due December 2021
Derivative [Line Items]
Interest rate on senior notes			4.20%
Interest Rate Contract
Derivative [Line Items]
Number of instruments held | instrument			2