Cash, Cash Equivalents, and Restricted Cash (Schedule of Cash, Cash Equivalents and Restricted Cash) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Restricted Cash And Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 176,622	$ 308,560
Restricted cash - current asset	62,926	31,671
Total cash, cash equivalents, and restricted cash	242,185	342,808	$ 229,615	$ 141,120
Securitization Escrow Accounts [Member] | Restricted Cash - Current Asset [Member]
Restricted Cash And Cash Equivalents Items [Line Items]
Restricted cash - current asset	62,773	31,507
Payment and Performance Bonds [Member] | Restricted Cash - Current Asset [Member]
Restricted Cash And Cash Equivalents Items [Line Items]
Restricted cash - current asset	153	164
Surety Bonds and Workers Compensation [Member] | Other Assets - Noncurrent [Member]
Restricted Cash And Cash Equivalents Items [Line Items]
Restricted cash - noncurrent asset	$ 2,637	$ 2,577