Intangible Assets - Finite Lived Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets, Net [Abstract]
Total amortized intangible assets, Gross Value	$ 32,309	$ 33,809
Total amortized intangible assets, Accumulated Amortization	(16,156)	(15,911)
Total amortized intangible assets, Net Value	16,153	17,898
Amortization expense	1,700	2,000	$ 2,200
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
Future amortization expense, 2016	1,700
Future amortization expense, 2017	1,700
Future amortization expense, 2018	1,600
Future amortization expense, 2019	1,400
Future amortization expense, thereafter	9,700
Permits [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Total amortized intangible assets, Gross Value	25,959	25,959
Total amortized intangible assets, Accumulated Amortization	(12,504)	(11,514)
Total amortized intangible assets, Net Value	13,455	14,445
Customer lists [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Total amortized intangible assets, Gross Value	2,200	2,200
Total amortized intangible assets, Accumulated Amortization	(1,467)	(1,174)
Total amortized intangible assets, Net Value	733	1,026
Covenants not to compete [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Total amortized intangible assets, Gross Value	50	50
Total amortized intangible assets, Accumulated Amortization	(26)	(24)
Total amortized intangible assets, Net Value	24	26
Acquired Backlog[Member]
Finite-Lived Intangible Assets, Net [Abstract]
Total amortized intangible assets, Gross Value		1,500
Total amortized intangible assets, Accumulated Amortization		(1,472)
Total amortized intangible assets, Net Value		28
Trade Names [Member]
Finite-Lived Intangible Assets, Net [Abstract]
Total amortized intangible assets, Gross Value	4,100	4,100
Total amortized intangible assets, Accumulated Amortization	(2,159)	(1,727)
Total amortized intangible assets, Net Value	$ 1,941	$ 2,373