Segment Information (Details)	3 Months Ended								6 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 segment	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($) segment	Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Contract revenues	$ 162,214,000	$ 140,162,000	$ 137,420,000	$ 138,757,000	$ 144,295,000	$ 164,017,000	$ 140,301,000	$ 129,623,000		$ 578,553,000	$ 578,236,000	$ 466,498,000
Number of reportable segments | segment									2	2	2
Intersegment Eliminations
Segment Reporting Information [Line Items]
Contract revenues										$ 0	$ 0
Heavy Civil Marine Construction Segment | Mexico and the Caribbean
Segment Reporting Information [Line Items]
Contract revenues										$ 9,400,000	$ 7,400,000