Derivative Financial Instruments (Fair Value of Derivatives by Balance Sheet Location) (Details) - USD ($) $ in Thousands		Mar. 31, 2025	Dec. 31, 2024
Derivatives, Fair Value [Line Items]
Accrued interest receivable		$ 20,800	$ 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]	577	1,529
Interest rate fair value hedge asset at fair value		698	1,477
Accrued interest receivable		75	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]	637	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 collar | 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 collar | Derivatives Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Interest rate cash flow hedge liability at fair value		39	30
Interest rate collar | Derivatives Designated as Hedging Instruments | Cash Flow Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		50,000	50,000
Interest rate contracts with customers | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		820,536	886,912
Interest rate contracts with customers | Derivatives Not Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Derivative assets not designated		4,392	2,468
Interest rate contracts with customers | Derivatives Not Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		39,355	51,372
Mirror interest rate contracts with counterparties | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		820,536	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		39,178	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		4,468	2,529
Risk participation agreements | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		329,827	343,935
Risk participation agreements | Derivatives Not Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Derivative assets not designated		36	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		45,349	20,238
Interest rate lock commitments | Derivatives Not Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Derivative assets not designated		819	248
Interest rate lock commitments | Derivatives Not Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		1	0
Forward sale commitments | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		79,973	52,100
Forward sale commitments | Derivatives Not Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Derivative assets not designated		3	163
Forward sale commitments | Derivatives Not Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		794	291
Derivative assets
Derivatives, Fair Value [Line Items]
Gross derivative asset positions		45,703	57,090
Less: derivative asset amounts offset	[2]	5,044	2,788
Derivative asset balances, net of offset		40,659	54,302
Less: collateral pledged, assets	[3]	0	0
Net amounts		40,659	54,302
Derivative liabilities
Derivatives, Fair Value [Line Items]
Gross derivative liability positions		45,294	54,451
Less: derivative liability amounts offset	[2]	5,044	2,788
Derivative liability balances, net of offset		40,250	51,663
Less: collateral pledged, liabilities	[3]	0	0
Net amounts		$ 40,250	$ 51,663

[1] The fair value of derivative assets includes accrued interest receivable of $75 thousand and $120 thousand, respectively, at March 31, 2025 and December 31, 2024. There was no accrued interest payable included in the fair value of derivative liabilities at March 31, 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.