Cash and Cash Equivalents and Short Term Investments - Summary of Amortized Cost And Recorded Basis of T-bills in Short Term Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Short-term investments	$ 105,256	$ 104,719

Amount of investment in debt security measured at amortized cost (held-to-maturity), classified as current.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26626-111562

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