Cash, Cash Equivalents, Marketable Securities, and Restricted Cash - Additional Information (Details) - USD ($)	3 Months Ended	9 Months Ended
Mar. 31, 2020	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019
Cash, Cash Equivalents, and Short-term Investments [Abstract]
Cash and cash equivalents		$ 210,631,000	$ 142,837,000	$ 166,319,000
Available-for-sale debt securities		298,451,000	309,903,000
Realized gain (loss) on debt securities	$ 0	0
Fair value of available-for-sale debt securities in unrealized loss positions		$ 117,700,000	$ 42,600,000

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes 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. Excludes cash and cash equivalents within disposal group and discontinued operation.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3044-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121566466&loc=d3e6676-107765

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.1)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant