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Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Dec. 31, 2017 | Sep. 30, 2018 | Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2016
Significant Accounting Policies [Line Items] |  |  |  |  |
Cash and cash equivalents held by foreign subsidiaries and branch offices |  | $ 7,300,000 | $ 7,300,000 |  |
Minimum credit limit |  |  | 30 days |  |
Extended credit terms for trade receivables |  |  | 60 days |  |
Accounts receivable |  | 14,323,000 | $ 14,323,000 | $ 9,435,000 |
Cumulative-effect adjustment to retained earnings |  | $ 400,000 | $ 400,000 |  |
U.S. income tax rate | 35.00% | 21.00% | 24.50% | 35.00% | 35.00%
Unrecorded excess tax benefits in additional paid-in-capital account |  |  | $ 0 |  |
Shipping and Handling |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Shipping and handling costs |  |  | 500,000 | $ 300,000 | $ 400,000
Customer one |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Trade account and financing receivable due |  | $ 9,000,000 | $ 9,000,000 |  |
Financing receivable |  |  |  | $ 8,100,000 |
Accounts receivable |  |  |  |  | $ 9,100,000
Customer Concentration Risk | Customer one | Sales Revenue, Net |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Percentage of company revenue |  |  | 10.40% | 17.80% | 18.50%

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