Revenues - Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Unbilled receivable	$ 24,733	$ 23,516
ASUS
Disaggregation of Revenue [Line Items]
Unbilled receivable	13,854	9,693
Receivable from the U.S. government	84,573	91,489
Contract assets	14,484	14,378
Contract liabilities	653	$ 1,352
Revenue, remaining performance obligation, amount	$ 4,000,000
ASUS | Maximum
Disaggregation of Revenue [Line Items]
Period of Fixed Price Contracts to Operate and Maintain Water Systems at Various Military Bases	50 years
Revenue, remaining performance obligation, expected timing of satisfaction, period	50 years