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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	$ 66,600	$ 64,568	$ 65,200	$ 63,018
Charge-offs	(7,974)	(6,825)	(24,450)	(19,251)
Recoveries	1,835	1,537	4,765	4,635
Provision	7,889	6,388	22,835	17,266
Balance, end of period	68,350	65,668	68,350	65,668
Allowance for loan losses for acquired loan portfolio	0	700	0	700
Provision expense and net charge-offs related to acquired loans	0	100	700	400
Commercial Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	24,428	25,222	25,444	25,545
Charge-offs	(574)	(637)	(2,991)	(1,723)
Recoveries	266	512	919	1,616
Provision	1,434	1,514	2,182	1,173
Balance, end of period	25,554	26,611	25,554	26,611
Consumer Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	35,523	31,471	33,375	29,253
Charge-offs	(6,979)	(6,046)	(19,742)	(16,409)
Recoveries	1,446	898	3,680	2,779
Provision	6,197	6,078	18,874	16,778
Balance, end of period	36,187	32,401	36,187	32,401
Residential Real Estate Mortgages [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	6,649	7,875	6,381	7,960
Charge-offs	(421)	(142)	(1,717)	(1,119)
Recoveries	123	127	166	240
Provision	258	(1,481)	1,779	(702)
Balance, end of period	6,609	6,379	6,609	6,379
Unallocated [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	0	0	0	260
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision	0	277	0	17
Balance, end of period	$ 0	$ 277	$ 0	$ 277