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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	$ 70,200	$ 65,700	$ 69,500	$ 65,200
Charge-offs	(8,557)	(8,082)	(17,231)	(16,476)
Recoveries	2,029	1,415	3,907	2,930
Provision	8,778	7,567	16,274	14,946
Balance, end of period	72,450	66,600	72,450	66,600
Commercial Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	28,190	24,727	27,606	25,444
Charge-offs	(907)	(1,123)	(1,712)	(2,417)
Recoveries	183	206	370	653
Provision	3,593	618	4,795	748
Balance, end of period	31,059	24,428	31,059	24,428
Consumer Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	36,973	34,769	36,830	33,375
Charge-offs	(7,442)	(6,261)	(15,129)	(12,763)
Recoveries	1,700	1,199	3,344	2,234
Provision	5,248	5,816	11,434	12,677
Balance, end of period	36,479	35,523	36,479	35,523
Residential Real Estate [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	5,037	6,204	5,064	6,381
Charge-offs	(208)	(698)	(390)	(1,296)
Recoveries	146	10	193	43
Provision	(63)	1,133	45	1,521
Balance, end of period	4,912	6,649	4,912	6,649
Acquired Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period			0
Charge-offs	100	$ 300	200	$ 700
Balance, end of period	$ 0		$ 0