Summary of Significant Accounting Policies (Cash and Cash Equivalents) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Cash and cash equivalents	$ 884,171	$ 70,629
Overnight money market funds	837,600	39,600
Restricted cash	$ 5,303	$ 64,035

Amount of cash and cash equivalents restricted as to withdrawal or usage. 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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-Name Accounting Standards Codification
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-SubTopic 210
-Section S99
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Name:	us-gaap_RestrictedCashAndCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant