Commitments and Contingencies - Schedule of Future Minimum Rental Payments Required Under Operating Leases in Place (Details) $ in Thousands	Sep. 30, 2018 USD ($)
Future minimum rental payments
2018	$ 4,861
2019	20,082
2020	13,928
2021	8,756
2022	8,544
Thereafter	19,579
Total	75,750
Sublease Income
2018	(109)
2019	(545)
2020	(871)
2021	(871)
2022	(871)
Thereafter	(2,178)
Total	(5,445)
Net Minimum Payments
2018	4,752
2019	19,537
2020	13,057
2021	7,885
2022	7,673
Thereafter	17,401
Total	$ 70,305

No definition

No definition available.

Name:	mc_FutureMinimumPaymentLeaseNetAbstract
Namespace Prefix:	mc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Total Amount of required minimum rental payments for net operating leases having an initial or remaining non-cancelable lease term.

+ References

No definition available.

+ Details

Name:	mc_OperatingLeasesFutureMinimumPaymentsDueCurrentNet
Namespace Prefix:	mc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractually required future rental payments receivable on non-cancelable subleasing arrangements in the fifth fiscal year.

+ References

No definition available.

+ Details

Name:	mc_OperatingLeasesFutureMinimumPaymentsDueInFiveYearsFutureMinimumSubleaseRentals
Namespace Prefix:	mc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of required minimum rental payments for net operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fifth fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	mc_OperatingLeasesFutureMinimumPaymentsDueInFiveYearsNet
Namespace Prefix:	mc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractually required future rental payments receivable on non-cancelable subleasing arrangements in the fourth fiscal year.

+ References

No definition available.

+ Details

Name:	mc_OperatingLeasesFutureMinimumPaymentsDueInFourYearsFutureMinimumSubleaseRentals
Namespace Prefix:	mc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of required minimum rental payments for net operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fourth fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	mc_OperatingLeasesFutureMinimumPaymentsDueInFourYearsNet
Namespace Prefix:	mc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractually required future rental payments receivable on non-cancelable subleasing arrangements in next twelve months.

+ References

No definition available.

+ Details

Name:	mc_OperatingLeasesFutureMinimumPaymentsDueInNextTwelveMonthsFutureMinimumSubleaseRentals
Namespace Prefix:	mc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of required minimum rental payments for net operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the next fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	mc_OperatingLeasesFutureMinimumPaymentsDueInNextTwelveMonthsNet
Namespace Prefix:	mc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractually required future rental payments receivable on non-cancelable subleasing arrangements in the third fiscal year.

+ References

No definition available.

+ Details

Name:	mc_OperatingLeasesFutureMinimumPaymentsDueInThreeYearsFutureMinimumSubleaseRentals
Namespace Prefix:	mc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of required minimum rental payments for net operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the third fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	mc_OperatingLeasesFutureMinimumPaymentsDueInThreeYearsNet
Namespace Prefix:	mc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractually required future rental payments receivable on non-cancelable subleasing arrangements in second fiscal year.

+ References

No definition available.

+ Details

Name:	mc_OperatingLeasesFutureMinimumPaymentsDueInTwoYearsFutureMinimumSubleaseRentals
Namespace Prefix:	mc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of required minimum rental payments for net operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the second fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	mc_OperatingLeasesFutureMinimumPaymentsDueInTwoYearsNet
Namespace Prefix:	mc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractually required future rental payments receivable on non-cancelable subleasing arrangements after the fifth fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	mc_OperatingLeasesFutureMinimumPaymentsDueThereafterFutureMinimumSubleaseRentals
Namespace Prefix:	mc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of required minimum rental payments for net operating leases having an initial or remaining non-cancelable lease term in excess of one year due after the fifth fiscal year following the latest fiscal year.

+ References

No definition available.

+ Details

Name:	mc_OperatingLeasesFutureMinimumPaymentsDueThereafterNet
Namespace Prefix:	mc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

+ References

No definition available.

+ Details

Name:	mc_SubLeaseIncomeNetAbstract
Namespace Prefix:	mc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 10
-Section 55
-Paragraph 40
-Subparagraph (Note 3)
-URI http://asc.fasb.org/extlink&oid=82846649&loc=d3e38371-112697

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41502-112717

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41502-112717

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 10
-Section 55
-Paragraph 40
-Subparagraph (Note 3)
-URI http://asc.fasb.org/extlink&oid=82846649&loc=d3e38371-112697

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractually required future rental payments receivable on noncancelable subleasing arrangements.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueFutureMinimumSubleaseRentals
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of required minimum rental payments for operating leases having an initial or remaining non-cancelable lease term in excess of one year due after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

Name:	us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant