Acquisitions - Amortization Expense of Acquired Intangible Assets (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 8,800	$ 3,700	$ 2,000
Kenny
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense	7,560
Cost of Revenue - Construction | Kenny
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense	6,400
Cost of Revenue - Large Project Construction | Kenny
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense	435
Selling, General and Administrative Expenses | Kenny
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 725