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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	$ 65,700	$ 64,318	$ 65,200	$ 63,018
Charge-offs	(8,082)	(5,867)	(16,476)	(12,426)
Recoveries	1,415	1,337	2,930	3,098
Provision	7,567	4,780	14,946	10,878
Balance, end of period	66,600	64,568	66,600	64,568
Allowance for loan losses for acquired loan portfolio	0	800	0	800
Provision expense and net charge-offs related to acquired loans	300	100	700	400
Commercial Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	24,727	25,299	25,444	25,545
Charge-offs	(1,123)	(649)	(2,417)	(1,086)
Recoveries	206	339	653	1,104
Provision	618	233	748	(341)
Balance, end of period	24,428	25,222	24,428	25,222
Consumer Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	34,769	31,035	33,375	29,253
Charge-offs	(6,261)	(4,950)	(12,763)	(10,363)
Recoveries	1,199	907	2,234	1,881
Provision	5,816	4,479	12,677	10,700
Balance, end of period	35,523	31,471	35,523	31,471
Residential Real Estate Mortgages [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	6,204	7,984	6,381	7,960
Charge-offs	(698)	(268)	(1,296)	(977)
Recoveries	10	91	43	113
Provision	1,133	68	1,521	779
Balance, end of period	6,649	7,875	6,649	7,875
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	0	0	(260)
Balance, end of period	$ 0	$ 0	$ 0	$ 0