Summary of Significant Accounting Policies - Concentrations of Credit Risk and Restricted Cash (Details) $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($) item	Dec. 31, 2018 USD ($) item
Restricted cash
Cash securing letter of credit \| $	$ 210	$ 210
Cash and cash equivalents \| Credit concentration
Concentration risk
Number of financial institutions holding cash, cash equivalents and short-term investments \| item	2	2

Carrying amount as of the balance sheet date of cash collateral held for borrowed securities, for which the cash is restricted as to withdrawal or usage.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.1)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.(a),2)
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

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