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, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period	$ 64,318	$ 65,359	$ 63,018	$ 66,359
Charge-offs	(5,867)	(5,368)	(12,426)	(11,048)
Recoveries	1,337	1,070	3,098	2,108
Provision	4,780	3,898	10,878	7,540
Balance, end of period	64,568	64,959	64,568	64,959
Allowance for loan losses for acquired loan portfolio	800	1,900	800	1,900
Provision expense and net charge-offs related to acquired loans	100	100	400	700
Commercial Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period	25,299	31,278	25,545	32,433
Charge-offs	(649)	(584)	(1,086)	(1,382)
Recoveries	339	280	1,104	514
Provision	233	(2,648)	(341)	(3,239)
Balance, end of period	25,222	28,326	25,222	28,326
Consumer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period	31,035	26,156	29,253	26,720
Charge-offs	(4,950)	(4,275)	(10,363)	(8,653)
Recoveries	907	697	1,881	1,445
Provision	4,479	5,736	10,700	8,802
Balance, end of period	31,471	28,314	31,471	28,314
Residential Real Estate Mortgages [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period	7,984	7,698	7,960	7,130
Charge-offs	(268)	(509)	(977)	(1,013)
Recoveries	91	93	113	149
Provision	68	999	779	2,015
Balance, end of period	7,875	8,281	7,875	8,281
Unallocated [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance, beginning of period	0	227	260	76
Charge-offs	0	0	0	0
Recoveries	0	0	0	0
Provision	0	(189)	(260)	(38)
Balance, end of period	$ 0	$ 38	$ 0	$ 38