Premises and Equipment schedule (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Gross land, buildings and equipment	$ 923,097	$ 863,779
Less accumulated depreciation and amortization	552,460	530,660
Net land, buildings and equipment	370,637	333,119
Depreciation expense	30,800	28,600	$ 29,100
Repairs and maintenance expense	17,000	16,900	16,400
Interest Expense Capitalized on Construction Projects	0	0	$ 0
Land [Member]
Property, Plant and Equipment [Line Items]
Gross land, buildings and equipment	91,678	91,603
Building and improvements [Member]
Property, Plant and Equipment [Line Items]
Gross land, buildings and equipment	566,177	545,510
Equipment [Member]
Property, Plant and Equipment [Line Items]
Gross land, buildings and equipment	237,047	226,666
Right of use leased assets [Member]
Property, Plant and Equipment [Line Items]
Gross land, buildings and equipment	$ 28,195	$ 0