Commitments and Contingencies - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013 Linear_Feet	Mar. 25, 2013 Cases
Loss Contingencies [Line Items]
Installation of a reactive iron wall covering area	250
Estimated plan cost for initial construction	$ 688,000
Expected operation and maintenance expenses	$ 1,997,000
Estimated period	30 years
Unresolved cases		32
Massachusetts [Member]
Loss Contingencies [Line Items]
Number of cases pending	234
Number of cases terminated	167
Settlement agreements, cases	35
Washington [Member]
Loss Contingencies [Line Items]
Number of cases pending	1