Summary of Significant Accounting Policies - Expense recognition (Details) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Summary of Significant Accounting Policies
Advertising expenses	$ 8,000	$ 4,000	$ 1,008,000	$ 54,000

Amount charged to advertising expense, net of adjustment, for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

No definition available.

Name:	dvd_AdvertisingExpenseNet
Namespace Prefix:	dvd_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration