Property and Equipment Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Long Lived Assets Held-for-sale [Line Items]
Depreciation expense		$ 28,400	$ 24,800	$ 26,900
Assets disposed of in 2017			5,400
Proceeds from sale of property and equipment		3,234	6,826	2,152
Loss on Disposition of Property Plant Equipment		$ (3,306)	(674)	(1,579)
Impairment of long-lived assets held-for-use			1,000	$ 6,400
Insurance claims pending	$ 900		900
Heavy Civil Marine Construction Segment
Long Lived Assets Held-for-sale [Line Items]
Proceeds from sale of property and equipment			4,500
Loss on Disposition of Property Plant Equipment	$ 100		$ 900