Derivative Financial Instruments (Fair Value of Derivatives by Balance Sheet Location) (Details) - USD ($) $ in Thousands		Mar. 31, 2022	Dec. 31, 2021
Derivative Financial Instruments, Assets [Member]
Derivatives, Fair Value [Line Items]
Gross derivative asset positions		$ 30,199	$ 35,855
Amounts offset in balance sheet	[1]	13,961	2,167
Net amounts presented in balance sheet		16,238	33,688
Collateral pledged	[2]	0	0
Net amounts		16,238	33,688
Derivative Financial Instruments, Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross derivative liability positions		47,900	40,703
Amounts offset in balance sheet	[1]	13,961	2,167
Net amounts presented in balance sheet		33,939	38,536
Collateral pledged	[2]	10,848	34,539
Net amounts		23,091	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		201	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		18,947	5,301
Not Designated as Hedging Instrument [Member] | Interest rate swaps with customers [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		7,088	32,361
Not Designated as Hedging Instrument [Member] | Interest rate swaps with customers [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		21,656	2,015
Not Designated as Hedging Instrument [Member] | Mirror swaps with counterparties [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		21,518	2,001
Not Designated as Hedging Instrument [Member] | Mirror swaps with counterparties [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		7,141	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		2	2
Not Designated as Hedging Instrument [Member] | Interest rate lock commitments [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		407	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		85	0
Not Designated as Hedging Instrument [Member] | Forward sale commitments [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets not designated		985	54
Not Designated as Hedging Instrument [Member] | Forward sale commitments [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liabilities not designated		$ 69	$ 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.