v3.7.0.1

Receivables - Receivables Available for Sale and Sold under Factoring Agreements (Detail) - USD ($) $ in Millions | Dec. 31, 2016 | Dec. 31, 2015
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Receivables [Abstract] |  |
Available for sale | $ 44.3 | $ 47.3
Sold | $ 36.5 | $ 37.7

X
- Definition The amount of outstanding receivables that had been sold as of reporting date. + References No definition available. + Details
Name: | mpg_TradeReceivablesSoldAmount
Namespace Prefix: | mpg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

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- Definition The face amount of accounts receivable that will be sold to other entities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=65884687&loc=d3e4428-111522 + Details
Name: | us-gaap_TradeReceivablesHeldForSaleAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant