Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Summary Of Significant Accounting Policies [Line Items]
Cash Equivalents Percentage Held in Us Government Backed Securities	99.00%	98.00%
ASU No. 2016-01
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect increase (net of taxes) in stockholders' equity	$ 4,059

Amount of the cumulative effect on retained earnings net of related income tax effect.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22663-107794

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Period Type:	duration