Restricted Cash (Schedule Of Cash, Cash Equivalents And Restricted Cash) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restricted Cash And Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 68,783	$ 146,109	$ 118,039
Restricted cash - short term	32,924	36,786
Total cash, cash equivalents, and restricted cash	104,295	185,970	146,619	$ 97,896
Securitization Escrow Accounts [Member] | Restricted Cash - Current Asset [Member]
Restricted Cash And Cash Equivalents Items [Line Items]
Restricted cash - short term	32,699	36,607	25,135
Payment and Performance Bonds [Member] | Restricted Cash - Current Asset [Member]
Restricted Cash And Cash Equivalents Items [Line Items]
Cash and cash equivalents	225	179	218
Surety Bonds and Workers Compensation [Member] | Other Assets - Noncurrent [Member]
Restricted Cash And Cash Equivalents Items [Line Items]
Restricted cash - long term	$ 2,588	$ 3,075	$ 3,227