Statements of Operations of Discontinued Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues and other income (expense)	$ 14,866	$ 9,340	$ 24,440	$ 21,415
Operating costs	13,110	12,198	23,334	23,537
Income tax expense (benefit)	15	36	93	81
Loss from discontinued operations, net of income taxes	(51)	(735)	(655)	(2,620)
Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues and other income (expense)	516	964	577	1,143
Operating costs	567	1,699	1,233	3,759
Earnings (loss) before income taxes	(51)	(735)	(656)	(2,616)
Income tax expense (benefit)			(1)	4
Loss from discontinued operations, net of income taxes	$ (51)	$ (735)	$ (655)	$ (2,620)

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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