Derivative Instruments - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended						6 Months Ended
	Aug. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2007 Agreement	Jun. 30, 2011	Jun. 30, 2008	Jun. 30, 2011 Interest Rate Swap Agreement One	Jun. 30, 2011 Interest Rate Swap Agreement Two	Dec. 31, 2007 Floating Rate Term Loan Due 2010	Jun. 30, 2011 Notes Issued Ten	Jun. 30, 2011 Notes Issued One	Dec. 31, 2007 Year 2013
Derivative [Line Items]
Long-term notes issued					$ 1,225,000,000	$ 1,100,000,000	$ 650,000,000			$ 325,000,000	$ 500,000,000
Variable rate basis					3-month London Interbank Offered Rate (LIBOR)			6-month LIBOR	6-month LIBOR
Interest rate spread above London Interbank Offered Rate (LIBOR)					1.25%			4.05%	8.03%
Length of interest rate swap agreement (In years)					3 years
Notional amount of interest rate swap agreement					325,000,000			500,000,000	150,000,000
Fixed interest rate under swap agreement					5.25%			6.50%	10.125%
Amount of pretax loss accumulated in Other Comprehensive Income related to interest rate swap reclassified to earnings				(12,075,000)
Notional amount for forward starting interest rate swap agreements					1,500,000,000
Payments for (Proceeds from) settlement of interest rate swap agreements	(25,382,000)	0	(23,387,000)	0	89,777,000
Estimated amount of pretax loss in AOCI related to interest rate swap that would be reclassified to earnings within the next 12 months													(5,157,000)
Number of forward starting interest rate swap agreements					15
Coupon rate of notes											6.50%	10.125%
Forward component of the settlement	23,387,000
Accrued interest income	$ 1,995,000