XML 43 R30.htm IDEA: XBRL DOCUMENT
v3.20.4

ACCUMULATED OTHER COMPREHENSIVE LOSS (Tables) | 12 Months Ended
--- | ---
Dec. 31, 2020
ACCUMULATED OTHER COMPREHENSIVE LOSS |
Schedule of accumulated other comprehensive loss | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | Unrealized | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | Gain (Loss) | ​ | ​ | ​
​ | ​ | Pension | ​ | on | ​ | ​ | ​
​ |  | Adjustment |  | Securities |  | Total
(in thousands) |  | ​ |  |  | ​ |  |  | ​ |
Balance at December 31, 2018 | ​ | $ | (2,178) | ​ | $ | 3 | ​ | $ | (2,175)
Adoption of accounting standard (Note 1) | ​ | ​ | (404) | ​ | ​ | (10) | ​ | ​ | (414)
Before-tax amount | ​ |  | (300) | ​ |  | 13 | ​ |  | (287)
Tax benefit | ​ |  | 66 | ​ |  | (3) | ​ |  | 63
Reclassification adjustment, net of taxes | ​ |  |  | ​ |  |  | ​ |  |
Amortization of net loss | ​ |  | 68 | ​ |  | — | ​ |  | 68
Net realized loss | ​ |  | — | ​ |  | (3) | ​ |  | (3)
Total activity in 2019 | ​ |  | (570) | ​ |  | (3) | ​ |  | (573)
Balance at December 31, 2019 | ​ | $ | (2,748) | ​ | $ | — | ​ | $ | (2,748)
Before-tax amount | ​ |  | 250 | ​ |  | ​ | ​ |  | 250
Tax expense | ​ |  | (30) | ​ |  | ​ | ​ |  | (30)
Reclassification adjustment, net of taxes | ​ |  |  | ​ |  | ​ | ​ |  |
Amortization of net loss | ​ |  | 76 | ​ |  | ​ | ​ |  | 76
Pension settlement loss | ​ |  | 505 | ​ |  | ​ | ​ |  | 505
Total activity in 2020 | ​ |  | 801 | ​ |  | ​ | ​ |  | 801
Balance at December 31, 2020 | ​ | $ | (1,947) | ​ | $ | — | ​ | $ | (1,947)

X
- Definition The entire disclosure of accumulated other comprehensive (loss) income. + References No definition available. + Details
Name: | mpx_AccumulatedOtherComprehensiveLossIncomeTextBlock
Namespace Prefix: | mpx_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTaxAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration