Property, Plant and Equipment - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property, Plant and Equipment [Line Items]
Amortization expense on assets recorded under capital leases	$ 1,200,000	$ 1,200,000	$ 1,900,000
Accumulated depreciation and amortization, Capital lease assets	173,915,000	154,725,000
Related Party
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization, Capital lease assets	4,800,000	4,200,000
Non-Related Party
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization, Capital lease assets	$ 4,400,000	$ 3,800,000