Derivative Financial Instruments (Fair Value of Derivatives by Balance Sheet Location) (Details) - USD ($) $ in Thousands		Sep. 30, 2025	Dec. 31, 2024
Derivatives, Fair Value [Line Items]
Accrued interest receivable		$ 21,000	$ 22,100
Interest rate swaps | Derivatives Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Interest rate cash flow hedge asset at fair value	[1]	211	1,529
Interest rate fair value hedge asset at fair value		254	1,477
Accrued interest receivable		78	120
Interest rate swaps | Derivatives Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Interest rate cash flow hedge liability at fair value	[1]	999	229
Interest rate fair value hedge liability at fair value		0	0
Accrued interest payable		0	0
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 swaps | Derivatives Designated as Hedging Instruments | Fair Value Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		100,000	100,000
Interest rate collars | Derivatives Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Interest rate cash flow hedge asset at fair value		0	0
Interest rate collars | Derivatives Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Interest rate cash flow hedge liability at fair value		26	30
Interest rate collars | Derivatives Designated as Hedging Instruments | Cash Flow Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		100,000	50,000
Interest rate floors | Derivatives Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Interest rate cash flow hedge asset at fair value		189	0
Interest rate floors | Derivatives Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Interest rate cash flow hedge liability at fair value		0	0
Interest rate floors | Derivatives Designated as Hedging Instruments | Cash Flow Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		200,000	0
Interest rate contracts with customers | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		869,141	886,912
Interest rate contracts with customers | Derivatives Not Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Derivative assets not designated		6,722	2,468
Interest rate contracts with customers | Derivatives Not Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		29,572	51,372
Mirror interest rate contracts with counterparties | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		869,141	886,912
Mirror interest rate contracts with counterparties | Derivatives Not Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Derivative assets not designated		29,459	51,176
Mirror interest rate contracts with counterparties | Derivatives Not Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		6,792	2,529
Risk participation agreements | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		305,593	343,935
Risk participation agreements | Derivatives Not Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Derivative assets not designated		33	29
Risk participation agreements | Derivatives Not Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		0	0
Interest rate lock commitments | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		54,594	20,238
Interest rate lock commitments | Derivatives Not Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Derivative assets not designated		1,007	248
Interest rate lock commitments | Derivatives Not Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		3	0
Forward sale commitments | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		102,458	52,100
Forward sale commitments | Derivatives Not Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Derivative assets not designated		130	163
Forward sale commitments | Derivatives Not Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		675	291
Derivative assets
Derivatives, Fair Value [Line Items]
Gross derivative asset positions		38,005	57,090
Less: derivative asset amounts offset	[2]	7,192	2,788
Derivative asset balances, net of offset		30,813	54,302
Less: collateral pledged, assets	[3]	0	0
Net amounts		30,813	54,302
Derivative liabilities
Derivatives, Fair Value [Line Items]
Gross derivative liability positions		38,067	54,451
Less: derivative liability amounts offset	[2]	7,192	2,788
Derivative liability balances, net of offset		30,875	51,663
Less: collateral pledged, liabilities	[3]	0	0
Net amounts		$ 30,875	$ 51,663

[1] The fair value of derivative assets includes accrued interest receivable of $78 thousand and $120 thousand, respectively, at September 30, 2025 and December 31, 2024. There was no accrued interest payable included in the fair value of derivative liabilities at September 30, 2025 or at December 31, 2024.

[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.