Comparison of Key Financial Covenants and Current Compliance (Detail)	Dec. 31, 2011
Financing Activities and Borrowing Arrangements [Line Items]
Permitted leverage ratio, maximum	0.32
Minimum interest coverage ratio	53.96
Covenant Requirement
Financing Activities and Borrowing Arrangements [Line Items]
Permitted leverage ratio, maximum	3.00
Minimum interest coverage ratio	4.00