Segment Reporting - Summary of Reconciliation of Non-GAAP Measure (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating income	$ 12,315	$ 9,534	$ 11,905	$ 11,740	$ 4,614	$ 13,047	$ 13,810	$ 14,257	$ 45,494	$ 45,728	$ 51,829
Payments to Acquire Property, Plant, and Equipment									(10,408)	(9,989)	(7,952)
Total OCF									50,253	57,353	63,211
Non-GAAP measure [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Operating income									45,494	45,728	51,829
Plus: Depreciation, amortization, accretion and impairment									15,167	21,614	19,334
Total EBITDA									60,661	67,342	71,163
Payments to Acquire Property, Plant, and Equipment									(10,408)	(9,989)	(7,952)
Total OCF									$ 50,253	$ 57,353	$ 63,211