Restatement of Condensed Consolidated Financial Statements - Summary of Adjustments to Previously Issued Consolidated Statements of Comprehensive Income (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2012 Non-affiliates [Member]	Sep. 30, 2012 Non-affiliates [Member]	Sep. 30, 2012 Affiliates [Member]	Sep. 30, 2012 Affiliates [Member]	Sep. 30, 2013 Scenario, Previously Reported [Member]	Sep. 30, 2013 Scenario, Previously Reported [Member]	Sep. 30, 2013 Scenario, Previously Reported [Member] Non-affiliates [Member]	Sep. 30, 2013 Scenario, Previously Reported [Member] Non-affiliates [Member]	Sep. 30, 2013 Scenario, Adjustment [Member]	Sep. 30, 2013 Scenario, Adjustment [Member]	Sep. 30, 2013 Scenario, Adjustment [Member] Non-affiliates [Member]	Sep. 30, 2013 Scenario, Adjustment [Member] Non-affiliates [Member]	Sep. 30, 2013 Scenario, Adjustment [Member] Affiliates [Member]	Sep. 30, 2013 Scenario, Adjustment [Member] Affiliates [Member]	Sep. 30, 2013 Restated [Member]	Sep. 30, 2013 Restated [Member]	Sep. 30, 2013 Restated [Member] Non-affiliates [Member]	Sep. 30, 2013 Restated [Member] Non-affiliates [Member]	Sep. 30, 2013 Restated [Member] Affiliates [Member]	Sep. 30, 2013 Restated [Member] Affiliates [Member]
Condensed Income Statements, Captions [Line Items]
Operating revenues, non-affiliates	$ 96,658	$ 272,613					$ 83,841	$ 272,657			$ (1,414)	$ (1,535)					$ 82,427	$ 271,122
Operating revenues, affiliates	92	96									1,414	1,535					1,414	1,535
Cost of services and sales			36,277	111,409	69	193			44,720	117,371			(11,642)	(11,959)	11,642	11,959			33,078	105,412	11,642	11,959
(Gain) loss on disposal of assets, net	(2,559)	(2,140)					(132,109)	(131,483)			(74,894)	(74,894)					(207,003)	(206,377)
AWN excess distribution							(2,867)	(2,867)			2,867	2,867
Total operating expenses (income)	72,111	228,243					(59,855)	91,968			(72,027)	(72,027)					(131,882)	19,941
Operating income	24,639	44,466					143,696	180,689			72,027	72,027					215,723	252,716
Income before income tax expense	14,380	14,971					131,836	148,373			72,027	72,027					203,863	220,400
Income tax expense	(6,136)	(6,385)					(54,238)	(29,613)			(29,718)	(29,718)					(83,956)	(59,331)
Net income	8,244	8,586					77,598	118,760			42,309	42,309					119,907	161,069
Total comprehensive income	$ 8,546	$ 7,603					$ 78,513	$ 121,057			$ 42,309	$ 42,309					$ 120,822	$ 163,366
Net income per share:
Basic	$ 0.18	$ 0.19					$ 1.65	$ 2.55			$ 0.89	$ 0.91					$ 2.54	$ 3.46
Diluted	$ 0.17	$ 0.19					$ 1.33	$ 2.09			$ 0.72	$ 0.72					$ 2.05	$ 2.81