Summary of Significant Accounting Policies (Schedule of Cash and Cash Equivalents) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash and cash equivalents	$ 374,289	$ 193,685
Restricted cash	77,563	8,416
Total cash, cash equivalents and restricted cash	451,852	202,101	$ 119,863	$ 197,648
General Corporate Purposes
Cash and cash equivalents	210,841	43,760
Joint Venture
Cash and cash equivalents	$ 163,448	$ 149,925

Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as current. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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