Derivative Financial Instruments (Fair Value of Derivatives by Balance Sheet Location) (Details) - USD ($) $ in Thousands		Jun. 30, 2023	Dec. 31, 2022
Derivatives, Fair Value [Line Items]
Accrued interest receivable		$ 20,200	$ 17,600
Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Notional amount		100,000	320,000
Interest rate swaps [Member] | Designated as Cash Flow Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional amount		100,000	320,000
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]	1,964	548
Accrued interest receivable		153	24
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]	0	31,178
Accrued interest payable			856
Interest rate contracts with customers [Member]
Derivatives, Fair Value [Line Items]
Notional amount		875,201	935,099
Interest rate contracts with customers [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional amount		875,201	935,099
Interest rate contracts with customers [Member] | Not Designated as Hedging Instrument [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		91	32
Interest rate contracts with customers [Member] | Not Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		66,670	68,137
Mirror interest rate contracts with counterparties [Member]
Derivatives, Fair Value [Line Items]
Notional amount		875,201	935,099
Mirror interest rate contracts with counterparties [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional amount		875,201	935,099
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		66,295	67,797
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		91	61
Risk participation agreements [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional amount		289,237	282,191
Risk participation agreements [Member] | Not Designated as Hedging Instrument [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		0	0
Risk participation agreements [Member] | Not Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		1	2
Interest rate lock commitments [Member]
Derivatives, Fair Value [Line Items]
Notional amount		30,136	12,201
Interest rate lock commitments [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional amount		30,136	12,201
Interest rate lock commitments [Member] | Not Designated as Hedging Instrument [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		347	144
Interest rate lock commitments [Member] | Not Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		16	4
Forward sale commitments [Member]
Derivatives, Fair Value [Line Items]
Notional amount		66,285	23,150
Forward sale commitments [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Notional amount		66,285	23,150
Forward sale commitments [Member] | Not Designated as Hedging Instrument [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		284	58
Forward sale commitments [Member] | Not Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		115	150
Derivative assets[Member]
Derivatives, Fair Value [Line Items]
Gross derivative asset positions		68,981	68,579
Less: derivative asset amounts offset	[2]	91	23,524
Derivative asset balances, net of offset		68,890	45,055
Less: collateral pledged	[3]	0	0
Net amounts		68,890	45,055
Derivative liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross derivative liability positions		66,893	99,532
Less: derivative liability amounts offset	[2]	91	23,524
Derivative liability balances, net of offset		66,802	76,008
Less: collateral pledged	[3]	0	7,716
Net amounts		$ 66,802	$ 68,292

[1] The fair value of derivative assets includes accrued interest receivable of $153 thousand and $24 thousand, respectively, at June 30, 2023 and December 31, 2022. The fair value of derivative liabilities includes accrued interest payable $856 thousand at December 31, 2022.

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

[3] Collateral 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.