Fair Value Measurement - Summary of Changes in Fair Value of Company's Level 3 Financial Liabilities (Details) - Level 3 - Trade-In Guarantee $ in Thousands  | 
6 Months Ended | 
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 Jun. 30, 2019  
USD ($) 
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| Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] | |
| Beginning Balance | $ 268 | 
| Recognition of revenue | $ (268) | 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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- Definition Amount of sales of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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