Depreciation, Amortization and Accretion - Summary of Depreciation, Amortization and Accretion (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Depreciation, Amortization And Accretion [Abstract]
Depreciation Expense	$ 2,066	$ 2,127	$ 6,167	$ 6,496
Amortization Expense	1,007	1,120	3,153	3,615
Accretion Expense	156	166	467	497
Total	$ 3,229	$ 3,413	$ 9,787	$ 10,608