Summary of Significant Accounting Policies (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2019
Cash paid for:
Interest	$ 3,743	$ 2,832	$ 1,864
Income taxes	33,401	38,144	$ 29,349
Contracts in progress
Costs incurred on contracts in progress	1,574,460	1,288,330
Estimated earnings, net of losses	300,514	253,641
Less—Billings to date	(1,958,567)	(1,617,860)
Less—Unbilled accounts receivable	(37,180)
Contracts in progress	(120,773)	(75,889)
Costs and estimated earnings in excess of billings	10,213	30,116
Billings in excess of costs and estimated earnings	$ (130,986)	(106,005)
Period during which progress billings or contract price can be withheld until completion of work	6 months
Retention receivable	$ 80,800	68,700
Retention payable	$ 13,700	$ 11,900
ASU 2016-02
Recent Accounting Pronouncements
Operating lease, right-of-use assets				$ 75,000
Operating lease liability				$ 75,000