Fair Value Measurements - Stock Option Rollforward (Details) - Stock Option Liability $ in Thousands	9 Months Ended
Sep. 30, 2020 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 43,026
Change in fair value	(9,656)
Amortization of grant date fair value	5,422
Settlement of stock options	(896)
Exercise of stock options	(235)
Ending balance	$ 37,661

Fair Value, Measurement With Unobservable Inputs Reconciliation, Recurring Basis, Liability, Amortization During Period

No definition available.

Name:	dxm_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityAmortizationDuringPeriod
Namespace Prefix:	dxm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Fair Value, Measurement With Unobservable Inputs Reconciliation, Recurring Basis, Liability, Exercise Of Stock Options In Period

+ References

No definition available.

+ Details

Name:	dxm_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityExerciseOfStockOptionsInPeriod
Namespace Prefix:	dxm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair Value, Measurement With Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included In Earnings, Excluding Amortization

+ References

No definition available.

+ Details

Name:	dxm_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarningsExcludingAmortization
Namespace Prefix:	dxm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

Amount of settlements of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=dxm_StockOptionLiabilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: