Derivative Instruments - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended	6 Months Ended
	Aug. 31, 2011	Dec. 31, 2007 Agreement	Jun. 30, 2011 Interest Rate Swap Agreement One	Jun. 30, 2011 Interest Rate Swap Agreement Two	Mar. 31, 2013 Year 2014	Jun. 30, 2011 Notes Issued Ten	Jun. 30, 2011 Notes Issued One
Derivative [Line Items]
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)	89,777,000
Number of forward starting interest rate swap agreements		15
Estimated amount of pretax loss in AOCI related to interest rate swap that would be reclassified to earnings within the next 12 months					4,915,000
Long-term notes issued						500,000,000
Coupon rate of notes						6.50%	10.125%
Variable rate basis			6-month LIBOR	6-month LIBOR
Interest rate spread above London Interbank Offered Rate (LIBOR)			4.05%	8.03%
Notional amount of interest rate swap agreement			500,000,000	150,000,000
Fixed interest rate under swap agreement			6.50%	10.125%
Forward component of the settlement	23,387,000
Accrued interest income	$ 1,995,000