Represents information regarding non-default rate of interest.

No definition available.

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Namespace Prefix:	mlr_
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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The average effective interest rate during the reporting period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
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+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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Balance Type:	na
Period Type:	duration

- Definition

Fair value of the amount outstanding under the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13433-108611

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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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Balance Type:	na
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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Details

Name:	us-gaap_LineOfCreditFacilityAxis=mlr_FirstTennesseeBankNationalAssociationMember
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- Details

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LONG-TERM OBLIGATIONS (Details) - USD ($) $ in Thousands	3 Months Ended
LONG-TERM OBLIGATIONS (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019	Dec. 20, 2018
Line of Credit Facility [Line Items]
Long-term obligations due within one year	$ 276	$ 368
First Tennessee Bank National Association \| Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility			$ 50,000
Debt instrument description of non-default rate of interest	LIBOR Rate plus 1.00% or 1.25% per annum, depending on the leverage ratio.
Line of credit outstanding borrowings	$ 29,998	4,998
First Tennessee Bank National Association \| Revolving Credit Facility \| Minimum
Line of Credit Facility [Line Items]
Variable interest rate in addition to reference rate	1.00%
Non-usage fee for current loan agreement in annual amount percentage	0.15%
First Tennessee Bank National Association \| Revolving Credit Facility \| Maximum
Line of Credit Facility [Line Items]
Variable interest rate in addition to reference rate	1.25%
Non-usage fee for current loan agreement in annual amount percentage	0.35%
Jige International S.A. \| Banque Europeenne Du Credit Mutuel
Line of Credit Facility [Line Items]
Unsecured fixed rate loan	$ 276	$ 368
Maturity date	Sep. 30, 2020
Interest rate per annum	0.30%