Depreciation, Amortization and Accretion - Summary of Depreciation, Amortization and Accretion (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Depreciation, Amortization And Accretion [Abstract]
Depreciation Expense	$ 2,127	$ 2,555	$ 6,496	$ 7,846
Amortization Expense	1,120	1,503	3,615	4,218
Accretion Expense	166	189	497	564
Total	$ 3,413	$ 4,247	$ 10,608	$ 12,628