Amount of the obligation recognized by withdrawing from a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

No definition available.

Name:	us-gaap_MultiemployerPlansWithdrawalObligation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Commitments and Contingencies (Details 2) (USD $) In Thousands, unless otherwise specified						12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Nov. 30, 2011	Dec. 31, 2012 Letters of credit	Dec. 31, 2011 Letters of credit	Dec. 31, 2012 Bonding	Dec. 31, 2011 Bonding	Dec. 31, 2010 Bonding
Commitments and contingencies
Total commercial letters of credit outstanding				$ 6,168	$ 11,798
Bid and completion bonds issued and outstanding						1,298,589	1,105,933	849,288
Withdrawal liability recorded	$ 7,500	$ 5,000	$ 7,500