Segment Reporting - Summary of Reconciliation of Non-GAAP Measure (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting [Abstract]
Operating income	$ 9,534	$ 13,047	$ 33,179	$ 41,114
Plus: Depreciation, amortization and accretion	3,858	4,724	11,487	13,845
Total EBITDA	13,392	17,771	44,666	54,959
Less: Purchases of property and equipment	(2,504)	(2,696)	(7,772)	(7,135)
Total OCF	$ 10,888	$ 15,075	$ 36,894	$ 47,824