Summary of Significant Accounting Policies - Reconciliation of cash, cash equivalents and restricted cash (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Summary of Significant Accounting Policies
Cash and cash equivalents	$ 424,395	$ 78,823
Restricted cash current	106,768	2,947
Restricted cash non-current	411	410
Cash, cash equivalents and restricted cash	$ 531,574	$ 82,180	$ 78,235	$ 81,959

Amount of cash and cash equivalents restricted as to withdrawal or usage, classified as noncurrent. 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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant