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Income Taxes - Additional Information (Detail) (USD $) | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Operating Loss Carryforwards [Line Items] |  |  |
Excess tax benefit obtained by company | $ 1,800,000 us-gaap_DeferredTaxExpenseFromStockOptionsExercised | $ 1,300,000 us-gaap_DeferredTaxExpenseFromStockOptionsExercised | $ 1,000,000 us-gaap_DeferredTaxExpenseFromStockOptionsExercised
Undistributed earnings of foreign subsidiaries | 1,600,000 us-gaap_UndistributedEarningsOfForeignSubsidiaries | 1,200,000 us-gaap_UndistributedEarningsOfForeignSubsidiaries |
Likelihood percentage of being realized upon ultimate settlement with the relevant tax authority | 50.00%mgrc_TaxBenefitLikelihoodPercentage |  |
Unrecognized tax benefits | 0 us-gaap_UnrecognizedTaxBenefits | 0 us-gaap_UnrecognizedTaxBenefits |
Changes in unrecognized benefits | 0 us-gaap_UnrecognizedTaxBenefitsPeriodIncreaseDecrease | 0 us-gaap_UnrecognizedTaxBenefitsPeriodIncreaseDecrease | 0 us-gaap_UnrecognizedTaxBenefitsPeriodIncreaseDecrease
Foreign [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
Company's foreign net operating losses for tax purposes | 1,000,000 us-gaap_OperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = us-gaap_ForeignCountryMember |  |
Foreign net operating loss carry forwards, expiration description | Begin to expire in 2022 |  |
State and Local Jurisdiction [Member] |  |  |
Operating Loss Carryforwards [Line Items] |  |  |
State and foreign tax credit carry forwards |  | $ 2,600,000 us-gaap_TaxCreditCarryforwardAmount / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember |

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- Definition Amount of deferred tax expense from write-off of the deferred tax asset related to deductible stock options at exercise. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 20 -Section 55 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=32706628&loc=d3e11283-113907 + Details
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- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319 + Details
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- Definition The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Carryforwards -URI http://asc.fasb.org/extlink&oid=6506874 + Details
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- Definition Amount of undistributed earnings of foreign subsidiaries intended to be permanently reinvested outside the country of domicile. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (b)(c) -URI http://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 740 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6479915&loc=d3e66715-112838 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 740 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6487024&loc=d3e29054-158556 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 995 -SubTopic 740 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6503627&loc=d3e59836-110443 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 25 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=29652012&loc=d3e28200-109314 + Details
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- Definition The net amount of all increases and decreases in unrecognized tax benefits for the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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