Benefit Plans (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2011 item	Dec. 31, 2010 item
Multiemployer plans
Number of employees employed by the entity	25,000	12,000	12,000
Expenses not reimbursed by clients and related to multiemployer defined benefit and defined contribution plans	$ 762	$ 710	$ 552
Red Zone | Maximum
Multiemployer plans
Multiemployer plans funded status (as a percent)	65.00%
Yellow Zone | Maximum
Multiemployer plans
Multiemployer plans funded status (as a percent)	80.00%
Green Zone | Minimum
Multiemployer plans
Multiemployer plans funded status (as a percent)	80.00%
Teamsters Local Union 727 | Minimum
Multiemployer plans
Entity's contributions as a percentage of total contributions	5.00%
Local 917 Pension Fund | Minimum
Multiemployer plans
Entity's contributions as a percentage of total contributions	5.00%
Multiemployer defined benefit pension plans | Teamsters Local Union 727
Multiemployer plans
Contributions	3,848	3,617	2,500
Multiemployer defined benefit pension plans | Local 917 Pension Fund
Multiemployer plans
Contributions	$ 97