Summary of Discontinued Operations Presented in Consolidated Statements of Operations and Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Acquisitions And Discontinued Operations [Line Items]
Operating revenues	$ 19,377	$ 173,447	$ 155,642
Total operating expenses, net	27,630	147,012	135,673
Operating income (loss)	(8,253)	26,435	19,969
Other income (expense), net	(168)	(270)	43
Income (loss) from discontinued operations before income taxes	(8,421)	26,165	20,012
Provision for income taxes	7,759	21,481	7,257
Income (loss) from discontinued operations, net of tax	$ (16,180)	$ 4,684	$ 12,755