Derivative Financial Instruments (Fair Value of Derivatives by Balance Sheet Location) (Details) - USD ($) $ in Thousands		Sep. 30, 2022	Dec. 31, 2021
Derivative Financial Instruments, Assets [Member]
Derivatives, Fair Value [Line Items]
Gross derivative asset positions		$ 72,614	$ 35,855
Amounts offset in balance sheet	[1]	24,516	2,167
Net amounts presented in balance sheet		48,098	33,688
Collateral pledged	[2]	0	0
Net amounts		48,098	33,688
Derivative Financial Instruments, Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross derivative liability positions		104,483	40,703
Amounts offset in balance sheet	[1]	24,516	2,167
Net amounts presented in balance sheet		79,967	38,536
Collateral pledged	[2]	8,542	34,539
Net amounts		71,425	3,997
Derivatives Designated as Cash Flow Hedging Instruments [Member] | Interest rate swaps [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets designated as a cash flow hedge		540	182
Derivatives Designated as Cash Flow Hedging Instruments [Member] | Interest rate swaps [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities designated as a cash flow hedge		32,936	5,301
Not Designated as Hedging Instrument [Member] | Interest rate contracts with customers [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		122	32,361
Not Designated as Hedging Instrument [Member] | Interest rate contracts with customers [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		71,028	2,015
Not Designated as Hedging Instrument [Member] | Mirror contracts with counterparties [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		70,679	2,001
Not Designated as Hedging Instrument [Member] | Mirror contracts with counterparties [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		122	32,480
Not Designated as Hedging Instrument [Member] | Risk participation agreements [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		0	1
Not Designated as Hedging Instrument [Member] | Risk participation agreements [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		0	2
Not Designated as Hedging Instrument [Member] | Interest rate lock commitments [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		204	1,256
Not Designated as Hedging Instrument [Member] | Interest rate lock commitments [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		186	0
Not Designated as Hedging Instrument [Member] | Forward sale commitments [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		1,069	54
Not Designated as Hedging Instrument [Member] | Forward sale commitments [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		$ 211	$ 905

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

[2] 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.