Depreciation, Amortization and Accretion - Summary of Depreciation, Amortization and Accretion (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Depreciation, Amortization And Accretion [Abstract]
Depreciation Expense	$ 2,044	$ 2,162	$ 4,101	$ 4,369
Amortization Expense	1,035	1,120	2,146	2,495
Accretion Expense	156	166	311	331
Total	$ 3,235	$ 3,448	$ 6,558	$ 7,195