Non-GAAP Financial Measures - Summary of Reconciliation of Non-GAAP measure (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Non-GAAP Financial Measures [Abstract]
Operating income	$ 6,550	$ 6,657	$ 5,621	$ 6,273	$ 4,618	$ 8,073	$ 7,368	$ 8,092	$ 25,100	$ 28,151	$ 45,494
Plus: Depreciation, amortization, accretion and impairment									13,970	16,677	15,167
EBITDA (as defined by the Company)									39,070	44,828	60,661
Less: Purchases of property and equipment									(6,374)	(7,679)	(10,408)
OCF (as defined by the Company)									$ 32,696	$ 37,149	$ 50,253