Fair Value Measurements (Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Assets:
Cash and cash equivalents maturity period (maximum)	3 months
Restricted and other investments, term (maximum)	5 years	5 years
Municipal Bonds
Assets:
Investments in lieu of retainage	$ 1,100	$ 1,300
US Government Agencies Securities
Assets:
Restricted and other investments	38,600	37,100
Corporate Debt Securities
Assets:
Investments in lieu of retainage	58,600
Restricted and other investments	46,000	46,700
Fair value measured on a recurring basis
Assets:
Cash and cash equivalents	316,499	202,197
Restricted cash	4,870	9,199
Restricted investments	85,075	84,355
Investments in lieu of retainage	85,559	86,328
Total	492,003	382,079
Fair value measured on a recurring basis | Level 1
Assets:
Cash and cash equivalents	316,499	202,197
Restricted cash	4,870	9,199
Restricted investments	0	0
Investments in lieu of retainage	25,949	27,472
Total	347,318	238,868
Fair value measured on a recurring basis | Level 2
Assets:
Cash and cash equivalents	0	0
Restricted cash	0	0
Restricted investments	85,075	84,355
Investments in lieu of retainage	59,610	58,856
Total	144,685	143,211
Fair value measured on a recurring basis | 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
Certificates of Deposit
Assets:
Restricted and other investments	500	600
Money Market Funds
Assets:
Investments in lieu of retainage	$ 25,900	27,500
Corporate Debt Securities
Assets:
Investments in lieu of retainage		$ 57,500