Derivative Financial Instruments (Fair Value of Derivatives by Balance Sheet Location) (Details) - USD ($) $ in Thousands		Sep. 30, 2024	Dec. 31, 2023
Derivatives, Fair Value [Line Items]
Accrued interest receivable		$ 22,600	$ 22,900
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]	307	802
Interest rate fair value hedge asset at fair value		33	0
Accrued interest receivable		218	239
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]	1,640	1,119
Interest rate fair value hedge liability at fair value		14	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	0
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		198	0
Interest rate collar | Derivatives Designated as Hedging Instruments | Cash Flow Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		50,000	0
Interest rate contracts with customers | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		902,068	938,872
Interest rate contracts with customers | Derivatives Not Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Derivative assets not designated		8,069	6,594
Interest rate contracts with customers | Derivatives Not Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		36,501	52,102
Mirror interest rate contracts with counterparties | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		902,068	938,872
Mirror interest rate contracts with counterparties | Derivatives Not Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Derivative assets not designated		36,346	51,859
Mirror interest rate contracts with counterparties | Derivatives Not Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		8,206	6,757
Risk participation agreements | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		340,822	321,055
Risk participation agreements | Derivatives Not Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Derivative assets not designated		58	66
Risk participation agreements | Derivatives Not Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		1	1
Interest rate lock commitments | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		41,191	20,980
Interest rate lock commitments | Derivatives Not Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Derivative assets not designated		684	504
Interest rate lock commitments | Derivatives Not Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		0	1
Forward sale commitments | Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Notional amount		76,213	50,117
Forward sale commitments | Derivatives Not Designated as Hedging Instruments | Other assets
Derivatives, Fair Value [Line Items]
Derivative assets not designated		78	18
Forward sale commitments | Derivatives Not Designated as Hedging Instruments | Other liabilities
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		513	711
Derivative assets
Derivatives, Fair Value [Line Items]
Gross derivative asset positions		45,575	59,843
Less: derivative asset amounts offset	[2]	8,528	7,877
Derivative asset balances, net of offset		37,047	51,966
Less: collateral pledged, assets	[3]	0	0
Net amounts		37,047	51,966
Derivative liabilities
Derivatives, Fair Value [Line Items]
Gross derivative liability positions		47,073	60,691
Less: derivative liability amounts offset	[2]	8,528	7,877
Derivative liability balances, net of offset		38,545	52,814
Less: collateral pledged, liabilities	[3]	0	0
Net amounts		$ 38,545	$ 52,814

[1] The fair value of derivative assets includes accrued interest receivable of $218 thousand and $239 thousand, respectively, at September 30, 2024 and December 31, 2023. There was no accrued interest payable included in the fair value of derivative liabilities at September 30, 2024 or at December 31, 2023.

[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.