Acquisition Proforma Net Income (Details) - Blue Hills Bancorp, Inc. [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Interest Income (Expense), after Provision for Loan Loss	$ 104,598	$ 94,804	$ 312,925	$ 271,644
Business Acquisition, Pro Forma Net Income (Loss)	$ 51,845	$ 38,804	$ 81,907	$ 110,517