Fair Value Measurements - Fair Value Inputs, Liabilities, Quantitative Information (Details) - Fair Value, Inputs, Level 3 $ in Thousands	Sep. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)
Revenue-based royalty
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Contingent consideration liabilities	$ 8,916	$ 10,661
Supply chain milestone
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Contingent consideration liabilities		13,593
Revenue milestones
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Contingent consideration liabilities	67,807	57,982
Regulatory approval
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Contingent consideration liabilities	2,885
Contingent receivable
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Contingent consideration asset	$ 506	$ 607
Discount rate \| Revenue-based royalty \| Minimum \| Discounted Cash Flow
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Unobservable inputs, contingent liability	0.13	0.099
Discount rate \| Revenue-based royalty \| Maximum \| Discounted Cash Flow
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Unobservable inputs, contingent liability	0.25	0.25
Discount rate \| Supply chain milestone \| Discounted Cash Flow
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Unobservable inputs, contingent liability		0.053
Discount rate \| Revenue milestones \| Minimum \| Discounted Cash Flow
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Unobservable inputs, contingent liability	0.13	0.033
Discount rate \| Revenue milestones \| Maximum \| Discounted Cash Flow
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Unobservable inputs, contingent liability	0.15	0.13
Discount rate \| Regulatory approval \| Discounted Cash Flow
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Unobservable inputs, contingent liability	0.039
Discount rate \| Contingent receivable \| Discounted Cash Flow
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Unobservable inputs, contingent receivable asset	0	0.10
Probability of milestone payment \| Supply chain milestone \| Discounted Cash Flow
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Unobservable inputs, contingent liability		0.95
Probability of milestone payment \| Regulatory approval \| Discounted Cash Flow
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Unobservable inputs, contingent liability	0.65
Probability of milestone payment \| Contingent receivable \| Discounted Cash Flow
Fair Value Inputs, Liabilities, Quantitative Information [Line Items] (Deprecated 2018-01-31)
Unobservable inputs, contingent receivable asset	1	0.67

Contingent Consideration, Asset, Measurement Input

No definition available.

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Namespace Prefix:	mmsi_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of asset recognized arising from contingent consideration in a business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 25
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6411-128476

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 35
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=116859824&loc=d3e6819-128478

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

+ Details

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

- Definition

Amount of liability recognized arising from contingent consideration in a business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 35
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=116859824&loc=d3e6819-128478

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 25
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6408-128476

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Value of input used to measure contingent consideration liability from business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- 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

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- Details

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- Details

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- Details

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