Cash, Cash Equivalents, and Restricted Cash (Schedule of Cash, Cash Equivalents and Restricted Cash) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restricted Cash And Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 308,560	$ 108,309	$ 143,444
Restricted cash - current asset	31,671	30,243
Total cash, cash equivalents, and restricted cash	342,808	141,120	178,300	$ 104,295
Securitization Escrow Accounts [Member] | Restricted Cash - Current Asset [Member]
Restricted Cash And Cash Equivalents Items [Line Items]
Restricted cash - current asset	31,507	30,046	32,261
Payment and Performance Bonds [Member] | Restricted Cash - Current Asset [Member]
Restricted Cash And Cash Equivalents Items [Line Items]
Restricted cash - current asset	164	197	203
Surety Bonds and Workers Compensation [Member] | Other Assets - Noncurrent [Member]
Restricted Cash And Cash Equivalents Items [Line Items]
Restricted cash - noncurrent asset	$ 2,577	$ 2,568	$ 2,392