Selected Financial Information Regarding Results of Operations of Charter Fleet Business (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on disposal of discontinued operations, before taxes		$ 257	$ (21,934)
Income (loss) from discontinued operations, net of tax	3,497	3,497	(12,812)
Charter Fleet Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues		8,184	44,849
Loss on disposal of discontinued operations, before taxes		257	(21,934)
Income before provision for income taxes		3,240	10,030
Total		3,497	(11,904)
Provision for income taxes			(2,908)
Income (loss) from discontinued operations, net of tax		$ 3,497	$ (14,812)