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Schedule II - Valuation and Qualifying Accounts (Detail) - Allowance for Doubtful Accounts [Member] - USD ($) | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Valuation and Qualifying Accounts Disclosure [Line Items] |  |  |  |
Balance at Beginning of Period |  | $ 224,000 | $ 159,000 | $ 153,000
Charge (Recovery) to Costs and Expenses |  | (144,000) | 65,000 | 6,000
Other Charges, Deductions | [1] | (21,000) |  |
Balance at End of Period |  | $ 59,000 | $ 224,000 | $ 159,000
[1] | Reflects uncollectible accounts written off, net of recoveries.

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- Definition Amount of valuation and qualifying accounts and reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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