Marketable Securities and Assets Measured at Fair Value - Fair Value of Marketable Securities (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Transfers from level 1 to level 2, Assets	$ 0	$ 0
Transfers from level 1 to level 2, Liabilities	0	0
Transfers from level 2 to level 1, Assets	0	0
Transfers from level 2 to level 1, Liabilities	0	0
Transfers in or out, Assets	0	0
Transfers in or out, Liabilities	0	0
Fair Value, Measurements, Recurring [Member]
Debt Securities, Available-for-sale [Line Items]
Assets, Fair Value Disclosure	747	747	$ 2,470
Fair Value, Measurements, Recurring [Member] \| Fair Value, Inputs, Level 2 [Member]
Debt Securities, Available-for-sale [Line Items]
Assets, Fair Value Disclosure	$ 747	$ 747	$ 2,470

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
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Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 820
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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