Selected Financial Information Regarding Results of Operations of Charter Fleet Business (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on disposal of discontinued operations	$ 257
Income from discontinued operations, net of tax	3,497		1,662
Charter Fleet Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	8,184	[1]	9,504
Gain on disposal of discontinued operations	257	[1]
Income before provision for income taxes	3,240	[1]	2,411
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax, Total	3,497	[1]	2,411
Provision for income taxes			(749)
Income from discontinued operations, net of tax	$ 3,497	[1]	$ 1,662

[1] Includes the charter fleet operations through March 19, 2012.