Stock-Based Compensation - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Share-based Payment Arrangement [Abstract]
Fair value of units awarded	$ 57.8	$ 38.1

Share-based Compensation Arrangement by Share-based Payment Award, Grants in Period, Fair Value

No definition available.

Name:	wex_ShareBasedCompensationArrangementByShareBasedPaymentAwardGrantsInPeriodFairValue
Namespace Prefix:	wex_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration