Fair Value Measurements (Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Assets:
Cash and cash equivalents maturity period (maximum)	3 months
Fair Value, Measurements, Recurring
Assets:
Cash and cash equivalents	$ 259,351	$ 202,197
Restricted cash	14,480	9,199
Restricted investments	91,556	84,355
Investments in lieu of retainage	88,328	86,328
Total	453,715	382,079
Fair Value, Measurements, Recurring | Level 1
Assets:
Cash and cash equivalents	259,351	202,197
Restricted cash	14,480	9,199
Restricted investments	0	0
Investments in lieu of retainage	20,100	27,472
Total	293,931	238,868
Fair Value, Measurements, Recurring | Level 2
Assets:
Cash and cash equivalents	0	0
Restricted cash	0	0
Restricted investments	91,556	84,355
Investments in lieu of retainage	68,228	58,856
Total	159,784	143,211
Fair Value, Measurements, Recurring | Level 3
Assets:
Cash and cash equivalents	0	0
Restricted cash	0	0
Restricted investments	0	0
Investments in lieu of retainage	0	0
Total	0	0
Money Market Funds
Assets:
Investments in lieu of retainage	20,100	27,500
Debt Securities | Fair Value, Measurements, Recurring | Level 1
Assets:
Investments in lieu of retainage	$ 68,200	$ 58,900