Retirement Benefit Plans (Contributions and Funding Status of the Fund) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Retirement Benefits [Abstract]
Contributions by Webster Bank	$ 614	$ 690	$ 340
Funded Status of the Plan at December 31,	At least 80 percent	At least 80 percent