Allowance for Loan Losses and Credit Quality of Loans, Allowance for Loan Losses by Portfolio Segments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	$ 72,165	$ 72,450	$ 72,505	$ 69,500
Charge-offs	(8,015)	(7,764)	(24,901)	(24,995)
Recoveries	1,891	2,093	5,353	6,000
Provision	6,324	6,026	19,408	22,300
Balance, end of period	72,365	72,805	72,365	72,805
Commercial Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	33,152	31,059	32,759	27,606
Charge-offs	(865)	(823)	(2,783)	(2,535)
Recoveries	132	410	344	780
Provision	1,021	1,086	3,120	5,881
Balance, end of period	33,440	31,732	33,440	31,732
Consumer Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	36,534	36,479	37,178	36,830
Charge-offs	(6,976)	(6,818)	(21,336)	(21,947)
Recoveries	1,746	1,602	4,887	4,946
Provision	5,031	6,044	15,606	17,478
Balance, end of period	36,335	37,307	36,335	37,307
Residential Real Estate [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	2,479	4,912	2,568	5,064
Charge-offs	(174)	(123)	(782)	(513)
Recoveries	13	81	122	274
Provision	272	(1,104)	682	(1,059)
Balance, end of period	2,590	3,766	2,590	3,766
Acquired Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period			0
Charge-offs	0	$ 0	(100)	$ (100)
Balance, end of period	$ 0		$ 0