Accounts Receivable, Net of Allowance (Schedule of Accounts Receivable, Net of Allowance) (Details) - USD ($) $ in Thousands	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accounts Receivable, Net of Allowance
Contract billings	$ 669,700				$ 598,200
Retainage	162,200				159,300
Cost and earnings in excess of billings	485,600				392,900
Accounts receivable, gross	1,317,500				1,150,400
Less allowance for doubtful accounts	(13,900)				(15,700)	$ (11,300)
Accounts receivable, net	$ 1,303,552	$ 1,385,678	$ 1,280,250	$ 1,185,236	$ 1,134,693