Fair Value Measurements (Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Dec. 31, 2022
Assets:
Cash and cash equivalents maturity period (maximum)	3 months
Fair value measured on a recurring basis
Assets:
Cash and cash equivalents	$ 263,545	$ 259,351
Restricted cash	10,914	14,480
Restricted investments	97,293	91,556
Investments in lieu of retention	92,214	88,328
Total	463,966	453,715
Fair value measured on a recurring basis | Level 1
Assets:
Cash and cash equivalents	263,545	259,351
Restricted cash	10,914	14,480
Restricted investments	0	0
Investments in lieu of retention	17,917	20,100
Total	292,376	293,931
Fair value measured on a recurring basis | Level 2
Assets:
Cash and cash equivalents	0	0
Restricted cash	0	0
Restricted investments	97,293	91,556
Investments in lieu of retention	74,297	68,228
Total	171,590	159,784
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 retention	0	0
Total	0	0
Debt Securities | Fair value measured on a recurring basis | Level 2
Assets:
Investments in lieu of retention	74,300	68,200
Money Market Funds | Fair value measured on a recurring basis | Level 1
Assets:
Investments in lieu of retention	$ 17,900	$ 20,100