Derivative Financial Instruments (Fair Value of Derivatives by Balance Sheet Location) (Details) - USD ($) $ in Thousands		Mar. 31, 2024	Dec. 31, 2023
Derivatives, Fair Value [Line Items]
Accrued interest receivable		$ 23,800	$ 22,900
Interest rate swaps [Member] | Designated as Cash Flow Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional amount		120,000	120,000
Interest rate swaps [Member] | Designated as Cash Flow Hedging Instruments [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Interest rate cash flow hedge asset at fair value	[1]	1,970	802
Accrued interest receivable		233	239
Interest rate swaps [Member] | Designated as Cash Flow Hedging Instruments [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Interest rate cash flow hedge liability at fair value	[1]	132	1,119
Accrued interest payable		0	0
Interest rate contracts with customers [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional amount		944,336	938,872
Interest rate contracts with customers [Member] | Not Designated as Hedging Instrument [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		3,880	6,594
Interest rate contracts with customers [Member] | Not Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		61,806	52,102
Mirror interest rate contracts with counterparties [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional amount		944,336	938,872
Mirror interest rate contracts with counterparties [Member] | Not Designated as Hedging Instrument [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		61,570	51,859
Mirror interest rate contracts with counterparties [Member] | Not Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		3,980	6,757
Risk participation agreements [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional amount		325,172	321,055
Risk participation agreements [Member] | Not Designated as Hedging Instrument [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		49	66
Risk participation agreements [Member] | Not Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		1	1
Interest rate lock commitments [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional amount		40,189	20,980
Interest rate lock commitments [Member] | Not Designated as Hedging Instrument [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		754	504
Interest rate lock commitments [Member] | Not Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		3	1
Forward sale commitments [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional amount		73,330	50,117
Forward sale commitments [Member] | Not Designated as Hedging Instrument [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		57	18
Forward sale commitments [Member] | Not Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		605	711
Derivative assets[Member]
Derivatives, Fair Value [Line Items]
Gross derivative asset positions		68,280	59,843
Less: derivative asset amounts offset	[2]	4,112	7,877
Derivative asset balances, net of offset		64,168	51,966
Less: collateral pledged	[3]	0	0
Net amounts		64,168	51,966
Derivative liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross derivative liability positions		66,527	60,691
Less: derivative liability amounts offset	[2]	4,112	7,877
Derivative liability balances, net of offset		62,415	52,814
Less: collateral pledged	[3]	0	0
Net amounts		$ 62,415	$ 52,814

[1] The fair value of derivative assets includes accrued interest receivable of $233 thousand and $239 thousand, respectively, at March 31, 2024 and December 31, 2023. There was no accrued interest payable included in the fair value of derivative liabilities at March 31, 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.