Balance Sheet Offsetting (Details) - USD ($)		Dec. 31, 2018	Dec. 31, 2017
Derivative Assets [Member]
Gross derivative assets		$ 13,892,000	$ 7,006,000
Less amounts offset in Consolidated Balance Sheets, derivative assets		10,732,000	5,238,000
Net amounts presented in Consolidated Balance Sheets, derivative assets		3,160,000	1,768,000
Less collateral pledged, derivatives assets	[1]	0	0
Net amounts		3,160,000	1,768,000
Derivative Liabilities [Member]
Gross derivative liabilities		13,118,000	6,841,000
Less amounts offset in Consolidated Balance Sheets, derivative liabilities		10,732,000	5,238,000
Net amounts presented in Consolidated Balance Sheets, derivative liabilities		2,386,000	1,603,000
Less collateral pledged, derivative liabilities	[1]	1,460,000	1,039,000
Net amounts		926,000	564,000
Other assets [Member] | Interest rate caps [Member]
Gross derivative assets		20,000	25,000
Other assets [Member] | Interest rate swaps [Member]
Gross derivative assets		903,000	213,000
Other assets [Member] | Interest rate floors [Member]
Gross derivative assets		37,000	110,000
Other liabilities [Member] | Interest rate caps [Member]
Gross derivative liabilities		0	0
Other liabilities [Member] | Interest rate swaps [Member]
Gross derivative liabilities		0	14,000
Other liabilities [Member] | Interest rate floors [Member]
Gross derivative liabilities		0	0
Other liabilities [Member] | Interest rate swaps with customers [Member]
Gross derivative assets		5,340,000	2,857,000
Gross derivative liabilities		7,719,000	3,884,000
Other liabilities [Member] | Mirror swaps with counterparties [Member]
Gross derivative assets		7,592,000	3,801,000
Gross derivative liabilities		5,392,000	2,917,000
Other liabilities [Member] | Foreign exchange contracts [Member]
Gross derivative assets		0	0
Gross derivative liabilities		$ 7,000	$ 26,000

[1] Collateral pledged to derivative counterparties 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.