Multiemployer Pension Withdrawal (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2013 Location	Dec. 31, 2012	Jun. 30, 2011
Multiemployer Pension Withdrawal [Abstract]
Number of locations	8
Multiemployer pension withdrawal expense (income)		$ 31,683
Total payments		41,186
Annual payment		2,059
Payment term		20 years
Risk free rate (in hundredths)		2.54%
Amortization of present value discount	209
Multiemployer pension withdrawal liability	31,892
Estimated liability under multiemployer collective bargaining agreements			$ 1,846