Selected Financial Information Regarding Results of Operations of Charter Fleet Business (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2012		Jun. 30, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total income from discontinued operations, net of tax	$ 3,610	$ 3,497		$ 5,272
Charter Fleet Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues	11,062	8,184	[1]	20,566
Income before provision for income taxes	2,330	3,497	[1]	4,741
Provision for income taxes	720			1,469
Total income from discontinued operations, net of tax	$ 1,610	$ 3,497	[1]	$ 3,272

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