Prepaid Expenses and Other Current Assets (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Prepaid expenses and other current assets
Current deferred tax asset	$ 29,129	$ 31,426
Restricted cash	102	17,994
Prepaid vehicle licenses	46,784	47,045
Prepaid operating taxes	13,322	12,477
Prepaid real estate rent	4,351	7,030
Prepaid contract incentives	4,789	5,612
Prepaid software maintenance costs	3,928	3,490
Prepaid benefits	1,313	0
Prepaid insurance	8,810	14,003
Prepaid sales commissions	7,908	9,385
Other	13,498	14,583
Total	$ 133,934	$ 163,045