Derivative Financial Instruments (Fair Value of Derivatives by Balance Sheet Location) (Details) - USD ($) $ in Thousands		Mar. 31, 2026	Dec. 31, 2025
Derivatives, Fair Value [Line Items]
Accrued interest receivable		$ 19,500	$ 20,100
Interest rate swaps | Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Accrued interest receivable		23	35
Accrued interest payable		49	23
Interest rate swaps | Derivatives Designated as Hedging Instruments | Cash Flow Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		120,000	120,000
Interest rate cash flow hedge asset at fair value	[1]	341	126
Interest rate cash flow hedge liability at fair value	[1]	470	979
Interest rate swaps | Derivatives Designated as Hedging Instruments | Fair Value Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		100,000	100,000
Interest rate fair value hedge asset at fair value		921	335
Interest rate fair value hedge liability at fair value		0	0
Interest rate collars | Derivatives Designated as Hedging Instruments | Cash Flow Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		100,000	100,000
Interest rate cash flow hedge asset at fair value		0	0
Interest rate cash flow hedge liability at fair value		3	17
Interest rate floors | Derivatives Designated as Hedging Instruments | Cash Flow Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		200,000	200,000
Interest rate cash flow hedge asset at fair value		116	125
Interest rate cash flow hedge liability at fair value		0	0
Interest rate contracts with customers | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		846,233	882,941
Derivative assets not designated as hedging instruments		4,690	6,326
Derivative liabilities not designated as hedging instruments		28,875	27,959
Mirror interest rate contracts with counterparties | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		846,233	882,941
Derivative assets not designated as hedging instruments		28,755	27,857
Derivative liabilities not designated as hedging instruments		4,783	6,392
Risk participation agreements | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		298,536	304,854
Derivative assets not designated as hedging instruments		40	28
Derivative liabilities not designated as hedging instruments		1	1
Interest rate lock commitments | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		40,650	30,373
Derivative assets not designated as hedging instruments		593	603
Derivative liabilities not designated as hedging instruments		13	12
Forward sale commitments | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		83,715	90,813
Derivative assets not designated as hedging instruments		334	13
Derivative liabilities not designated as hedging instruments		440	828
Derivative assets
Derivatives, Fair Value [Line Items]
Gross derivative assets		35,790	35,413
Less: derivative asset amounts offset	[2]	5,240	6,643
Derivative asset balances, net of offset		30,550	28,770
Less: collateral pledged, derivative assets	[3]	0	0
Net amounts		30,550	28,770
Derivative liabilities
Derivatives, Fair Value [Line Items]
Gross derivative liabilities		34,585	36,188
Less: derivative liability amounts offset	[2]	5,240	6,643
Derivative liability balances, net of offset		29,345	29,545
Less: collateral pledged, derivative liabilities	[3]	0	0
Net amounts		$ 29,345	$ 29,545

[1] The fair value of derivative assets includes accrued interest receivable of $23 thousand and $35 thousand, respectively, at March 31, 2026 and December 31, 2025. The fair value of derivative liabilities includes accrued interest payable of $49 thousand and $23 thousand, respectively, March 31, 2026 and December 31, 2025.

[2] Interest rate risk management contracts and loan related derivative contracts with counterparties are subject to master netting arrangements.

[3] Collateral contractually required to be pledged to derivative counterparties is in the form of cash. Washington Trust may need to post additional collateral in the future in proportion to potential increases in unrealized loss positions.