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MARKETABLE SECURITIES - Amortized cost basis, fair value and net unrealized gains on available-for-sale securities (Details 2) $ in Thousands	Dec. 31, 2018 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	$ 7,674
Fair Value	7,665
Net Unrealized Losses	(9)
Municipal Obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	1,490
Fair Value	1,490
Net Unrealized Losses	0
Corporate Obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost Basis	6,184
Fair Value	6,175
Net Unrealized Losses	$ (9)

X

- Definition

Amount, after tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

No definition available.

+ Details

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Namespace Prefix:	mpx_
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Balance Type:	debit
Period Type:	instant

X

- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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X

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

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- 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.

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