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:	us-gaap_RestrictedCashAndCashEquivalents
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Summary of Significant Accounting Polices - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	$ 9,899	$ 15,294
Restricted cash	477	113
Total	10,376	15,407	$ 16,482
Cash
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	2,530	4,390
Money market fund
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	5,432	5,956
Corporate debt securities
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	$ 1,937	1,948
Reverse repurchase agreements
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents		$ 3,000