Acquisitions and Dispositions - Acquisition-Related Expense (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Business Combinations [Abstract]
Due diligence, professional fees and other transaction costs	$ 0	$ 148
Adjustments to fair value of contingent consideration liabilities	(542)	305
Acquisition-related expense, net	$ (542)	$ 453

This element represents acquisition-related costs incurred in connection with business combinations which costs have been expensed during the period. This also includes adjustments to the fair value of the initial purchase price allocation for acquisitions including, but not limited to, changes in contingent consideration liabilities and other liabilities, accounts receivable, inventory, fixed assets, other assets, and other acquisition-related intangible assets. Acquisition-related costs also include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

No definition available.

Name:	mg_AcquisitionRelatedCostsAndFairValueAdjustmentsToInitialPurchasePriceAllocation
Namespace Prefix:	mg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration