Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $)	6 Months Ended	9 Months Ended
	Jun. 30, 2012	Sep. 30, 2012 Y	Sep. 30, 2011
Derivative [Line Items]
U.S. Treasury Note, maturity term (in years)		10
Proceeds from or (payments to) settlement of interest rate protection agreement		$ (65,500,000)	$ 9,910,000
Ineffective portion of derivative instruments	3,400,000
Settlement gains from interest rate protection agreement		2,200,000
Foreign currency forward contracts settled for a loss, amount		700,000
Net amount of settlement gains or losses on derivative instruments included in accumulated OCI, net gain amortized		5,700,000
Net amount of settlement gains or losses on derivative instruments included in accumulated OCI, net gain realized after tax		3,600,000
2003 Interest Rate Protection Agreement
Derivative [Line Items]
Proceeds from or (payments to) settlement of interest rate protection agreement		22,800,000
2008 Interest Rate Protection Agreement
Derivative [Line Items]
Proceeds from or (payments to) settlement of interest rate protection agreement		(4,400,000)
2010 Interest Rate Protection Agreement
Derivative [Line Items]
Proceeds from or (payments to) settlement of interest rate protection agreement		9,900,000
2011 Interest Rate Protection Agreement
Derivative [Line Items]
Proceeds from or (payments to) settlement of interest rate protection agreement		$ (65,500,000)