Schedule II - Valuation And Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Provision for doubtful accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at the Beginning of the Period	$ 2,600	$ 4,280	$ 0
Charged to Revenue, Cost or Expense	(487)	0	4,280
Deduction	1,702	1,680	0
Balance at the End of the Period	411	2,600	4,280
Reserve for losses on uncompleted contracts
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at the Beginning of the Period	10,925	22,770	0
Charged to Revenue, Cost or Expense	543	2,455	22,770
Deduction	9,995	14,300	0
Balance at the End of the Period	$ 1,473	$ 10,925	$ 22,770