Restatement of Condensed Consolidated Financial Statements - Summary of Adjustments To Previously Issued Consolidated Statements of Cash Flows (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended		3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Scenario, Previously Reported [Member]	Sep. 30, 2013 Scenario, Previously Reported [Member]	Sep. 30, 2013 Scenario, Adjustment [Member]	Sep. 30, 2013 Scenario, Adjustment [Member]	Sep. 30, 2013 Restated [Member]
Cash Flows from Operating Activities:
Net income		$ 8,586	$ 77,598	$ 118,760	$ 42,309	$ 42,309	$ 161,069
Adjustments to reconcile net income to net cash provided by operating activities:
Gain on sale/contribution of asset to AWN	(207,318)			(132,424)		(74,894)	(207,318)
AWN excess distribution			(2,867)	(2,867)	2,867	2,867
Deferred income taxes		6,385		29,015		29,718	58,733
Other non-cash expense, net		(2,042)		(1,710)		2,867	1,157
Net cash provided by operating activities		56,210		56,741		2,867	59,608
Cash Flows from Investing Activities:
AWN excess distribution				2,867		(2,867)
Net cash provided (used) by investing activities		$ (41,511)		$ 77,818		$ (2,867)	$ 74,951