Acquisition Preliminary Purchase Price Allocation (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Business Acquisition [Line Items]
Goodwill, Purchase Accounting Adjustments	$ 1,800
Finite-Lived Intangible Assets, Gross		48,570	49,370	34,370
Goodwill		53,598	55,419	9,900
Kenny [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Cash And Equivalents			53,185
Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Current Assets, Receivables			88,725
Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Costs And Estimated Earnings In Excess Of Billings			444
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory			731
Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Current Assets, Equity In Construction Joint Ventures			7,803
Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Current Assets, Other			6,039
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment			52,267
Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Customer Relationships			2,200
Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Intangible Assets, Other Than Goodwill			14,200
Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Current Liabilities, Accounts Payable			43,748
Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Current Liabilities, Billings In Excess Of Costs And Estimated Earnings			50,098
Business Combination, Recognized Identifiable Assets Acquired And Liabilities Assumed, Current Liabilities, Accrued Expenses And Other Current Liabilities			16,806
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value			15,326
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net			97,416
Goodwill			43,698
Total purchase price			141,114
Trade Names [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Assets, Gross		4,100	4,100
Order or Production Backlog [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Assets, Gross		7,900	7,900
Property, Plant and Equipment, Other Types [Member]
Business Acquisition [Line Items]
Goodwill, Purchase Accounting Adjustments	$ 1,100