XML 78 R66.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Investments - Breakdown of Investments with Unrealized Losses (Detail) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value | $ 39,093 | $ 101,600
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses | (902) | (1,781)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value | 21,484 | 5,701
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses | (461) | (351)
Total Fair Value | 60,577 | 107,301
Total Unrealized Losses | (1,363) | (2,132)
Deferred Compensation Plan Assets [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value | 1,922 | 294
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses | (81) | (12)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value | 262 | 245
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses | (15) | (30)
Total Fair Value | 2,184 | 539
Total Unrealized Losses | (96) | (42)
Corporate Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value | 16,015 | 32,562
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses | (58) | (166)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value | 6,112 | 2,722
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses | (97) | (8)
Total Fair Value | 22,127 | 35,284
Total Unrealized Losses | (155) | (174)
Municipal Fixed-Rate Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value | 230 | 8,936
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses |  | (37)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value | 1,165 |
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses | (22) |
Total Fair Value | 1,395 | 8,936
Total Unrealized Losses | (22) | (37)
Asset-Backed Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value | 4,941 | 2,986
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses | (17) | (14)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value | 179 |
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses | (3) |
Total Fair Value | 5,120 | 2,986
Total Unrealized Losses | (20) | (14)
Mortgage/Agency-Backed Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value | 3,062 | 7,842
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses | (8) | (81)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value | 1,673 | 1,239
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses | (38) | (10)
Total Fair Value | 4,735 | 9,081
Total Unrealized Losses | (46) | (91)
U.S. Government Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value | 2,754 | 26,449
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses | (26) | (270)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value | 11,549 |
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses | (148) |
Total Fair Value | 14,303 | 26,449
Total Unrealized Losses | (174) | (270)
Marketable Equity Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value | 10,169 | 21,607
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses | (712) | (1,200)
Continuous Unrealized Loss Position for 12 Months or Greater, Fair Value | 544 | 1,495
Continuous Unrealized Loss Position for 12 Months or Greater, Unrealized Losses | (138) | (303)
Total Fair Value | 10,713 | 23,102
Total Unrealized Losses | $ (850) | (1,503)
Foreign Government Bonds [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Continuous Unrealized Loss Position for Less than 12 Months, Fair Value |  | 924
Continuous Unrealized Loss Position for Less than 12 Months, Unrealized Losses |  | (1)
Total Fair Value |  | 924
Total Unrealized Losses |  | $ (1)

X
- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
Name: | us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
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_InvestmentTypeAxis=adtn_DeferredCompensationPlanAssetsMember
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_EquitySecuritiesMember
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: |