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Related Party Transactions - Additional Information (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Balance with Fund Manager	$ 17,735	$ 16,270
Minimum [Member]
Related Party Transaction [Line Items]
Percentage of stockholders controlling a related party	10.00%	10.00%
Maximum [Member]
Related Party Transaction [Line Items]
Fund management fee percent	0.35%
Other Income [Member]
Related Party Transaction [Line Items]
Investment income generated from mutual funds	$ 265
Cash and Cash Equivalents [Member]
Related Party Transaction [Line Items]
Balance with Fund Manager	8,827	$ 12,506
Marketable Securities [Member]
Related Party Transaction [Line Items]
Balance with Fund Manager	$ 8,908	$ 3,764

X

- Definition

Fund management fee percent.

+ References

No definition available.

+ Details

Name:	lgl_FundManagementFeePercent
Namespace Prefix:	lgl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Element represents the percentage of stockholders controlling a related party.

+ References

No definition available.

+ Details

Name:	lgl_PercentageOfStockholderControllingRelatedParty
Namespace Prefix:	lgl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The carrying amount of assets an investment adviser manages on behalf of investors.

+ References

No definition available.

+ Details

Name:	us-gaap_AssetsUnderManagementCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Amount of unrealized and realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

+ References

No definition available.

+ Details

Name:	us-gaap_MarketableSecuritiesGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_OtherIncomeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_CashAndCashEquivalentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_BalanceSheetLocationAxis=lgl_MarketableSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: