Stock-Based Compensation - Additional Information (Detail) - USD ($)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options Outstanding, Aggregate Intrinsic Value		$ 100,000
New Employees
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding awards	0	0
Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unamortized compensation cost, net of expected forfeitures	$ 200,000
Weighted average expected period over which the expense is to be recognized	1 year 4 months 24 days
Fair value of vested options and awards	$ 200,000	$ 300,000
Dividend yield (as a percent)	0.00%	0.00%
Stock options exercised	0	0
RSU's
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unamortized compensation cost, net of expected forfeitures	$ 300,000
Weighted average expected period over which the expense is to be recognized	9 months 18 days
Equity Incentive Plan 2010
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted (in shares)		0
Outstanding awards		172,000
Equity Incentive Plan 2010 \| RSU's
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total intrinsic value of the restricted stock units outstanding	$ 200,000	$ 200,000
Stock Incentive Plan 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares reserved for issuance	182,500
Stock Incentive Plan 2019 \| Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Maximum annual option grants or other awards to the entity's non-employee directors (in shares)	2,000
Maximum one-time grant of an option or other awards to the entity's non employee directors (in shares)	$ 6,000
Minimum percentage of voting rights required for applicability of a specific expiration term	10.00%
Maximum expiration term of options granted	5 years
Term of plan	10 years
Stock Incentive Plan 2019 \| Options \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of replacement options	3 years
Stock Incentive Plan 2019 \| Options \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period of replacement options	4 years

Fair Value equity-based compensation awards and options vested.

No definition available.

Name:	mosy_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsIncludingOptionsAggregateIntrinsicValueVested
Namespace Prefix:	mosy_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the maximum expiration term of awards granted applicable to holders of a specific percentage of voting rights of all classes of outstanding stock on the date of grant.

+ References

No definition available.

+ Details

Name:	mosy_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumExpirationTermApplicableToHoldersOfSpecificPercentageOfVotingRightsOfAllClasses
Namespace Prefix:	mosy_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the minimum percentage of voting rights of all classes of outstanding stock, on the date of grant, held by the persons to whom awards were granted for applicability of specific expiration term of options.

+ References

No definition available.

+ Details

Name:	mosy_ShareBasedCompensationArrangementByShareBasedPaymentAwardMinimumVotingPowerPercentageForApplicabilityOfSpecificExpirationTerm
Namespace Prefix:	mosy_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the shares reserved for grant under option or other awards to the entity's non-employee directors annually under the share-based compensation plan.

+ References

No definition available.

+ Details

Name:	mosy_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesReservedForAnnualGranttoNonEmployeeDirectors
Namespace Prefix:	mosy_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the shares reserved for one-time grant under option or other awards to the entity's non-employee directors under the share-based compensation plan.

+ References

No definition available.

+ Details

Name:	mosy_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesReservedForOneTimeGrantToNonEmployeeDirectors
Namespace Prefix:	mosy_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the term of share-based compensation plans.

+ References

No definition available.

+ Details

Name:	mosy_ShareBasedCompensationArrangementByShareBasedPaymentAwardTermOfPlan
Namespace Prefix:	mosy_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

+ References

+ Details

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

- Definition

Amount of cost to be recognized for option under share-based payment arrangement.

+ References

+ Details

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

- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsOutstandingNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of shares authorized for issuance under share-based payment arrangement.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Gross number of share options (or share units) granted during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

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

- Definition

Intrinsic value of outstanding award under share-based payment arrangement. Excludes share and unit options.

+ References

No definition available.

+ Details

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

- Definition

Number of share options (or share units) exercised during the current period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(2)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

Reference 3: 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(28))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: 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(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21463-112644

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_TitleOfIndividualAxis=mosy_NewEmployeesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=mosy_EmployeeAndDirectorsStockOptionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=mosy_EquityIncentivePlan2010Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=mosy_StockIncentivePlan2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- 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: