Deposits (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Time Certificates of Deposit [Abstract]
Time deposits greater than FDIC limit	$ 129.3	$ 75.1

Time deposits that meet or exceed the $250,000 FDIC limit

No definition available.

Name:	wash_TimedepositsgreaterthanFDIClimit
Namespace Prefix:	wash_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant