Cash and Cash Equivalents and Restricted Cash and Cash Equivalents (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2012 D M	Mar. 31, 2011	Dec. 31, 2011
Cash and Cash Equivalents and Restricted Cash and Cash Equivalents
Maximum original maturity period of highly liquid debt instruments to be considered as cash equivalents (in months)	3
Contractual maturity of revolving lines of credit that may be exceeded in certain cases (in days)	90
Restricted Cash and Cash Equivalents
Restricted cash and cash equivalents	$ 211,872		$ 308,039
Net change in restricted cash and cash equivalents	(97,639)	(20,611)
Fleet Debt
Restricted Cash and Cash Equivalents
Restricted cash and cash equivalents	126,500		213,600
Net change in restricted cash and cash equivalents	$ 87,100

The net cash inflow or outflow for the increase (decrease) associated with funds that are not available for withdrawal or use (such as funds held in escrow) and are associated with underlying transactions that are classified as investing activities.

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The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. This element is for unclassified presentations; for classified presentations there is a separate and distinct element.

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