Summary of Significant Accounting Policies (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Costs and estimated earnings in excess of billings beyond one year	$ 443,700,000
Contract Receivable Retainage, Estimated Collection After One Year, Percentage	30.00%
Contract Payable Retainage, Estimated Remittance After One Year, Percentage	19.00%
Goodwill impairment charge	$ 0
Indefinite lived intangible assets impairment charge	0
Net Cash Provided by (Used in) Investing Activities	(41,409,000)	$ (18,495,000)	$ (32,415,000)
Accounting Standards Update 2016-18 [Member]
Net Cash Provided by (Used in) Investing Activities	$ 45,700,000	$ (4,700,000)	$ (1,500,000)
Minimum [Member]
Estimated useful lives	3 years
Maximum [Member]
Estimated useful lives	40 years