Fund management fee percent.

No definition available.

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

- 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

- 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

- 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

- Definition

Amount of transactions with related party during the financial reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864

+ Details

Name:	us-gaap_RelatedPartyTransactionAmountsOfTransaction
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

Related Party Transactions - Additional Information (Details) - USD ($)		12 Months Ended
	May 02, 2019	Dec. 31, 2020	Dec. 31, 2019
Related Party Transaction [Line Items]
Balance with Fund Manager		$ 19,063,000	$ 14,536,000
Investment income generated from mutual funds		$ 139,000	$ 206,000
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		0.25%
Aggregate loan amount to cover expense related to SPAC IPO pursuant to promissory note	$ 150,000
Other Income [Member]
Related Party Transaction [Line Items]
Investment income generated from mutual funds		$ 213,000	$ 493,000
Cash and Cash Equivalents [Member]
Related Party Transaction [Line Items]
Balance with Fund Manager		13,283,000	8,915,000
Marketable Securities [Member]
Related Party Transaction [Line Items]
Balance with Fund Manager		$ 5,780,000	$ 5,621,000