Acquisitions - Preliminary Purchase Price Allocation (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Business Acquisition [Line Items]
Finite-Lived Intangible Assets, Gross	$ 49,370	$ 34,370
Goodwill	55,419	9,900
Kenny [Member]
Business Acquisition [Line Items]
Cash and cash equivalents	53,185
Receivables	88,725
Costs and estimates in excess of billings	444
Inventories	731
Equity in construction joint ventures	7,222
Other current assets	6,039
Property and equipment, net	51,126
Customer relationships	2,500
Total identifiable net assets acquired	15,000
Accounts payable	44,753
Billings in excess of costs and estimated earnings	50,098
Accrued expenses and other current liabilities	16,806
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value	14,788
Total identifiable net assets acquired	96,027
Goodwill	45,519
Total purchase price	$ 141,546