Summary of Significant Accounting Principles - Property and Equipment (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment
Assets classified as held-for-sale	$ 0.0	$ 0.0
Equipment improvement | Minimum
Property, Plant and Equipment
Property and equipment useful life	3 years
Equipment improvement | Maximum
Property, Plant and Equipment
Property and equipment useful life	7 years
Automobiles and trucks | Minimum
Property, Plant and Equipment
Property and equipment useful life	3 years
Automobiles and trucks | Maximum
Property, Plant and Equipment
Property and equipment useful life	5 years
Building and improvements | Minimum
Property, Plant and Equipment
Property and equipment useful life	5 years
Building and improvements | Maximum
Property, Plant and Equipment
Property and equipment useful life	30 years
Construction equipment | Minimum
Property, Plant and Equipment
Property and equipment useful life	3 years
Construction equipment | Maximum
Property, Plant and Equipment
Property and equipment useful life	15 years
Dredges and dredging equipment | Minimum
Property, Plant and Equipment
Property and equipment useful life	1 year
Dredges and dredging equipment | Maximum
Property, Plant and Equipment
Property and equipment useful life	15 years
Office equipment | Minimum
Property, Plant and Equipment
Property and equipment useful life	1 year
Office equipment | Maximum
Property, Plant and Equipment
Property and equipment useful life	5 years
Dry-docking capitalized costs | Minimum
Property, Plant and Equipment
Property and equipment useful life	3 years
Dry-docking capitalized costs | Maximum
Property, Plant and Equipment
Property and equipment useful life	15 years