Premises and Equipment (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Premises and Equipment
Cost	$ 468,387	$ 445,094
Accumulated Depreciation and Amortization	(337,461)	(331,589)
Net Book Value	130,926	113,505
Depreciation and amortization (including capital lease amortization) included in noninterest expense	13,000	12,900	$ 12,800
Premises
Premises and Equipment
Cost	331,566	321,144
Accumulated Depreciation and Amortization	(243,069)	(240,567)
Net Book Value	88,497	80,577
Impairment charge	0	0	$ 0
Equipment
Premises and Equipment
Cost	130,228	117,356
Accumulated Depreciation and Amortization	(90,319)	(87,021)
Net Book Value	39,909	30,335
Capital leases
Premises and Equipment
Cost	6,593	6,594
Accumulated Depreciation and Amortization	(4,073)	(4,001)
Net Book Value	$ 2,520	$ 2,593