XML 51 R66.htm IDEA: XBRL DOCUMENT
v3.20.1

Investments - Cash Equivalents and Investments held at Fair Value (Detail) - USD ($) $ in Thousands | Mar. 31, 2020 | Jan. 01, 2020 | Dec. 31, 2019
--- | --- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | $ 37,860 | $ 37,700 | $ 37,660
Marketable equity securities | 1,800 |  |
Fair Value, Measurements [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Other investments | 2,106 |  | 2,442
Total | 87,464 |  | 98,908
Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Other investments | 2,106 |  | 2,442
Total | 62,205 |  | 73,571
Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Total | 24,817 |  | 25,337
Fair Value, Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Total | 442 |  |
Money Market Funds [Member] | Fair Value, Measurements [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Cash equivalents | 4,826 |  | 1,309
Money Market Funds [Member] | Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Cash equivalents | 4,826 |  | 1,309
Commercial Paper [Member] | Fair Value, Measurements [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Cash equivalents | 500 |  |
Commercial Paper [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Cash equivalents | 500 |  |
Corporate Bonds [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 8,923 |  | 9,384
Corporate Bonds [Member] | Fair Value, Measurements [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 8,923 |  | 9,384
Corporate Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 8,923 |  | 9,384
Municipal Fixed-Rate Bonds [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 934 |  | 930
Municipal Fixed-Rate Bonds [Member] | Fair Value, Measurements [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 934 |  | 930
Municipal Fixed-Rate Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 934 |  | 930
Asset-Backed Bonds [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 5,993 |  | 6,890
Asset-Backed Bonds [Member] | Fair Value, Measurements [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 5,993 |  | 6,890
Asset-Backed Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 5,993 |  | 6,890
Mortgage/Agency-Backed Bonds [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 8,467 |  | 6,962
Mortgage/Agency-Backed Bonds [Member] | Fair Value, Measurements [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 8,467 |  | 6,962
Mortgage/Agency-Backed Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 8,467 |  | 6,962
U.S. Government Bonds [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 13,101 |  | 12,323
U.S. Government Bonds [Member] | Fair Value, Measurements [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 13,101 |  | 12,323
U.S. Government Bonds [Member] | Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 13,101 |  | 12,323
Other [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 442 |  |
Other [Member] | Fair Value, Measurements [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 442 |  |
Other [Member] | Fair Value, Measurements [Member] | Significant Unobservable Inputs (Level 3) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities | 442 |  |
Marketable Equity Securities - Various Industries [Member] | Fair Value, Measurements [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Marketable equity securities | 24,823 |  | 35,501
Marketable Equity Securities - Various Industries [Member] | Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Marketable equity securities | 24,823 |  | 35,501
Equity in Escrow [Member] | Fair Value, Measurements [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Marketable equity securities |  |  | 298
Equity in Escrow [Member] | Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Marketable equity securities |  |  | 298
Deferred Compensation Plan Assets [Member] | Fair Value, Measurements [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Marketable equity securities | 17,349 |  | 21,698
Deferred Compensation Plan Assets [Member] | Fair Value, Measurements [Member] | Quoted Prices in Active Market for Identical Assets (Level 1) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Marketable equity securities | $ 17,349 |  | 21,698
Foreign Government Bonds [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities |  |  | 371
Foreign Government Bonds [Member] | Fair Value, Measurements [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities |  |  | 371
Foreign Government Bonds [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities |  |  | 371
Variable Rate Demand Notes [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities |  |  | 800
Variable Rate Demand Notes [Member] | Fair Value, Measurements [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities |  |  | 800
Variable Rate Demand Notes [Member] | Fair Value, Measurements [Member] | Significant Other Observable Inputs (Level 2) [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available-for-sale debt securities |  |  | $ 800

X
- Definition Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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 + Details
Name: | us-gaap_AssetsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
Name: | us-gaap_CashAndCashEquivalentsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740 + Details
Name: | us-gaap_EquitySecuritiesFvNi
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investments classified as other. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1(f,g)) -URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_OtherInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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. + References No definition available. + Details
Name: | us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_MoneyMarketFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_CommercialPaperMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_CorporateBondSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_MunicipalBondsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_MortgageBackedSecuritiesIssuedByPrivateEnterprisesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_USTreasuryAndGovernmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_OtherDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=adtn_MarketableEquitySecuritiesVariousIndustriesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=adtn_EquityInEscrowMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=adtn_DeferredCompensationPlanAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_ForeignGovernmentDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_VariableRateDemandObligationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |