Fair Value Measurements (Assets And Liabilities Measured At Fair Value On Recurring Basis) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 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	$ 290,008	$ 259,351
Restricted cash	41,915	14,480
Restricted investments	98,361	91,556
Investments in lieu of retention	95,652	88,328
Total	525,936	453,715
Fair value measured on a recurring basis | Level 1
Assets:
Cash and cash equivalents	290,008	259,351
Restricted cash	41,915	14,480
Restricted investments	0	0
Investments in lieu of retention	16,283	20,100
Total	348,206	293,931
Fair value measured on a recurring basis | Level 2
Assets:
Cash and cash equivalents	0	0
Restricted cash	0	0
Restricted investments	98,361	91,556
Investments in lieu of retention	79,369	68,228
Total	177,730	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	79,400	68,200
Money Market Funds | Fair value measured on a recurring basis | Level 1
Assets:
Investments in lieu of retention	$ 16,300	$ 20,100