Commitments and Contingencies - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2012 Facility
Commitment And Contingencies [Line Items]
Number of sites cited as potentially responsible party	9
Previously Owned Facilities [Member]
Commitment And Contingencies [Line Items]
Number of sites with potential remediation obligations	8
Currently Owned Facilities [Member]
Commitment And Contingencies [Line Items]
Number of sites with potential remediation obligations	3