Property, Plant and Equipment - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Amortization expense on assets recorded under capital leases	$ 1,700,000	$ 1,700,000	$ 1,200,000
Accumulated depreciation and amortization, Capital lease assets	216,065,000	197,904,000
Related Party
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization, Capital lease assets	6,900,000	5,800,000
Non-Related Party
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization, Capital lease assets	$ 5,700,000	$ 5,100,000