Statements of Operations of Discontinued Operations (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
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Operating revenues	$ 9,777	$ 11,324	$ 34,219	$ 32,738
Operating costs	12,170	12,640	35,504	36,176
Income tax expense (benefit)	(7)	(60)	86	22
Discontinued Operations
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Operating revenues	310	759	885	1,901
Operating costs	482	1,221	1,712	4,979
Loss from discontinued operations before income taxes	(172)	(462)	(827)	(3,078)
Income tax expense (benefit)				4
Loss from discontinued operations, net of income taxes	$ (172)	$ (462)	$ (827)	$ (3,082)

Overall income (loss) from a disposal group that is classified as a component of the entity, before income tax, reported as a separate component of income before extraordinary items. Includes the following (before income tax): income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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Amount of income (loss) from a disposal group, net of income tax before extraordinary items allocable to noncontrolling interests. Includes, net of tax, income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

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