CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
CONSOLIDATED BALANCE SHEETS
Billed accounts receivable, allowance for credit losses (in dollars)	$ 7,993	$ 9,087
Unbilled accounts receivable, allowance for credit losses (in dollars)	815	784
Other receivables, allowance for credit losses (in dollars)	789	759
Costs and estimated earnings in excess of billings, allowance for credit losses (in dollars)	$ 34	$ 79
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	102,969,912	102,969,912
Common stock, shares issued	41,123,365	41,123,365
Treasury stock, shares	4,868,862	4,935,186