Related Party Transactions (Details) - Controlling Shareholders - Dropbox Charitable Foundation	3 Months Ended	12 Months Ended
Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2016 shareholder
Related Party Transaction [Line Items]
Number of controlling shareholders in related party transaction \| shareholder			2
Payments to related party \| $	$ 0	$ 0

Amount of transactions with related party during the financial reporting period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
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Name:	us-gaap_RelatedPartyTransactionAmountsOfTransaction
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration