The increase (decrease) during the period in the number of potential shares granted.

No definition available.

Name:	mmsi_PotentialSharesGrantedDuringPeriodIncreaseDecrease
Namespace Prefix:	mmsi_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-based compensation arrangement by share-based payment award, equity instruments other than options, conversion multiplying factor.

+ References

No definition available.

+ Details

Name:	mmsi_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsConversionMultiplyingFactor
Namespace Prefix:	mmsi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The annual target cash incentive amount for non-option equity instruments granted to participants.

+ References

No definition available.

+ Details

Name:	mmsi_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsAnnualTargetCashIncentive
Namespace Prefix:	mmsi_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the number of shares of common stock that each unit is equal to.

+ References

No definition available.

+ Details

Name:	mmsi_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesOfCommonStockForEachUnit
Namespace Prefix:	mmsi_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

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

- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ 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 (i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

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

- 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

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

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 (a)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

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

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ 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)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
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

Net number of non-option equity instruments granted to participants.

+ 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)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

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

- Definition

Net number of share options (or share units) granted during the 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)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

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

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ 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 (a)(2)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_ValuationTechniqueAxis=us-gaap_MarketApproachValuationTechniqueMember
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:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationTechniqueAxis=us-gaap_ValuationTechniqueDiscountedCashFlowMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=mmsi_CashSettledPerformanceSharesMember
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_GranteeStatusAxis=us-gaap_ShareBasedPaymentArrangementNonemployeeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Stock-Based Compensation Expense - Narrative (Details) - USD ($)		3 Months Ended			9 Months Ended
	Jun. 22, 2020	Sep. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation		$ 4,063,000		$ 2,626,000	$ 10,268,000	$ 6,915,000
Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation		$ 3,423,000		$ 2,003,000	$ 8,395,000	$ 5,212,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted in period (in shares)		112,500		107,000	328,994	1,200,000
Compensation cost not yet recognized		$ 25,000,000.0			$ 25,000,000.0
Compensation cost not yet recognized, period of recognition					2 years 9 months 18 days
Stock-Settled Performance-Based Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock units granted in period (in shares)					127,060
Allocated share-based compensation		800,000			$ 2,000,000.0
Compensation cost not yet recognized		3,300,000			$ 3,300,000
Compensation cost not yet recognized, period of recognition					1 year 6 months
Award vesting period					1 year
Number of shares of common stock for each unit					1
Stock-Settled Performance-Based Restricted Stock Units \| rTSR \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplying factor					75.00%
Stock-Settled Performance-Based Restricted Stock Units \| rTSR \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplying factor					125.00%
Stock-Settled Performance-Based Restricted Stock Units \| Performance period 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					1 year
Decrease in the potential shares of common stock to be granted			25,415
Stock-Settled Performance-Based Restricted Stock Units \| Performance period 1 \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplying factor					125.00%
Stock-Settled Performance-Based Restricted Stock Units \| Performance period 1 \| FCF \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplying factor					0.00%
Stock-Settled Performance-Based Restricted Stock Units \| Performance period 1 \| FCF \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplying factor			100.00%		100.00%
Stock-Settled Performance-Based Restricted Stock Units \| Performance period 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					2 years
Stock-Settled Performance-Based Restricted Stock Units \| Performance period 2 \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplying factor					250.00%
Stock-Settled Performance-Based Restricted Stock Units \| Performance period 2 \| FCF \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplying factor					0.00%
Stock-Settled Performance-Based Restricted Stock Units \| Performance period 2 \| FCF \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplying factor					200.00%
Stock-Settled Performance-Based Restricted Stock Units \| Performance period 3
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					3 years
Stock-Settled Performance-Based Restricted Stock Units \| Performance period 3 \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplying factor					250.00%
Stock-Settled Performance-Based Restricted Stock Units \| Performance period 3 \| FCF \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplying factor					0.00%
Stock-Settled Performance-Based Restricted Stock Units \| Performance period 3 \| FCF \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplying factor					200.00%
Cash-Settled Performance-Based Share-Based Awards (Liability Awards)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Target cash incentive		333,333			$ 333,333
Allocated share-based compensation		300,000			600,000
Compensation cost not yet recognized		1,300,000			$ 1,300,000
Compensation cost not yet recognized, period of recognition					1 year 7 months 6 days
Cash-Settled Performance-Based Share-Based Awards (Liability Awards) \| Performance period 1
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					1 year
Cash-Settled Performance-Based Share-Based Awards (Liability Awards) \| Performance period 1 \| rTSR
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplying factor					125.00%
Cash-Settled Performance-Based Share-Based Awards (Liability Awards) \| Performance period 2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					2 years
Cash-Settled Performance-Based Share-Based Awards (Liability Awards) \| Performance period 2 \| rTSR
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplying factor					250.00%
Cash-Settled Performance-Based Share-Based Awards (Liability Awards) \| Performance period 3
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period					3 years
Cash-Settled Performance-Based Share-Based Awards (Liability Awards) \| Performance period 3 \| rTSR
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Multiplying factor					250.00%
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period					1 year
Compensation cost not yet recognized		1,000,000.0			$ 1,000,000.0
Restricted Stock Units \| Selling, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated share-based compensation		$ 363,000			$ 395,000
Restricted Stock Units \| Non-employee members
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted	33,504