Selected Financial Information Regarding Results of Operations Attributable to Charter Fleet Business (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on disposal of discontinued operations, before taxes									$ (21,934)	$ (123,311)	$ (7,118)
Income (loss) from discontinued operations, net of tax	(19,271)	1,187	3,610	1,662	(592)	(40,030)	(2,657)	8,379	(12,812)	(34,900)	180,898
Charter Fleet Business
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Revenues									44,849	57,528	56,655
Loss on disposal of discontinued operations, before taxes									(21,934)	(27,690)
Income before provision for income taxes									10,030	8,081	(1,533)
Discontinued Operation, Income (Loss) from Discontinued Operation, before Income Tax, Total									(11,904)	(19,609)	(1,533)
Provision for income taxes									(2,908)	(2,711)	(3,534)
Income (loss) from discontinued operations, net of tax									$ (14,812)	$ (22,320)	$ (5,067)