Allowance for Loan Losses and Credit Quality of Loans, Allowance for Loan Losses by Portfolio Segments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	$ 71,405	$ 70,200	$ 72,505	$ 69,500
Charge-offs	(8,432)	(8,557)	(16,886)	(17,231)
Recoveries	1,915	2,029	3,462	3,907
Provision	7,277	8,778	13,084	16,274
Balance, end of period	72,165	72,450	72,165	72,450
Commercial Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	32,159	28,190	32,759	27,606
Charge-offs	(1,171)	(907)	(1,918)	(1,712)
Recoveries	118	183	212	370
Provision	2,046	3,593	2,099	4,795
Balance, end of period	33,152	31,059	33,152	31,059
Consumer Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	36,804	36,973	37,178	36,830
Charge-offs	(6,927)	(7,442)	(14,360)	(15,129)
Recoveries	1,742	1,700	3,141	3,344
Provision	4,915	5,248	10,575	11,434
Balance, end of period	36,534	36,479	36,534	36,479
Residential Real Estate [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	2,442	5,037	2,568	5,064
Charge-offs	(334)	(208)	(608)	(390)
Recoveries	55	146	109	193
Provision	316	(63)	410	45
Balance, end of period	2,479	4,912	2,479	4,912
Acquired Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period			0
Charge-offs	(100)	$ (100)	(100)	$ (200)
Balance, end of period	$ 0		$ 0