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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	$ 72,450	$ 66,600	$ 69,500	$ 65,200
Charge-offs	(7,764)	(7,974)	(24,995)	(24,450)
Recoveries	2,093	1,835	6,000	4,765
Provision	6,026	7,889	22,300	22,835
Balance, end of period	72,805	68,350	72,805	68,350
Commercial Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	31,059	24,428	27,606	25,444
Charge-offs	(823)	(574)	(2,535)	(2,991)
Recoveries	410	266	780	919
Provision	1,086	1,434	5,881	2,182
Balance, end of period	31,732	25,554	31,732	25,554
Consumer Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	36,479	35,523	36,830	33,375
Charge-offs	(6,818)	(6,979)	(21,947)	(19,742)
Recoveries	1,602	1,446	4,946	3,680
Provision	6,044	6,197	17,478	18,874
Balance, end of period	37,307	36,187	37,307	36,187
Residential Real Estate [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	4,912	6,649	5,064	6,381
Charge-offs	(123)	(421)	(513)	(1,717)
Recoveries	81	123	274	166
Provision	(1,104)	258	(1,059)	1,779
Balance, end of period	3,766	6,609	3,766	6,609
Acquired Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period			0
Charge-offs	0	$ 0	100	$ 700
Balance, end of period	$ 0		$ 0