Revenues - Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Unbilled receivable	$ 25,500	$ 27,147
Revenue, Remaining Performance Obligation, Amount	3,300,000
ASUS
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Unbilled receivable	16,378	14,835
Receivable from the U.S. government	72,444	79,818
Contract assets	12,571	9,587
Contract liabilities	$ 210	$ 257
Maximum | ASUS
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Explanation	46
Minimum | ASUS
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Explanation	33
Contracted Services | ASUS
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Period of Fixed Price Contracts to Operate and Maintain Water Systems at Various Military Bases	50 years