Allowance for Loan Losses and Credit Quality of Loans, Changes in Allowance for Loan Losses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	$ 63,018	$ 66,359	$ 69,434
Charge-offs	(29,299)	(26,087)	(27,473)
Recoveries	6,050	4,461	4,859
Provision	25,431	18,285	19,539
Balance, end of period	65,200	63,018	66,359
Commercial Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	25,545	32,433	35,090
Charge-offs	(4,592)	(5,718)	(9,414)
Recoveries	1,887	1,014	1,774
Provision	2,604	(2,184)	4,983
Balance, end of period	25,444	25,545	32,433
Consumer Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	29,253	26,720	27,694
Charge-offs	(23,364)	(18,140)	(16,642)
Recoveries	3,870	3,127	2,800
Provision	23,616	17,546	12,868
Balance, end of period	33,375	29,253	26,720
Residential Real Estate Mortgages [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	7,960	7,130	6,520
Charge-offs	(1,343)	(2,229)	(1,417)
Recoveries	293	320	285
Provision	(529)	2,739	1,742
Balance, end of period	6,381	7,960	7,130
Unallocated [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	260	76	130
Charge-offs	0	0	0
Recoveries	0	0	0
Provision	(260)	184	(54)
Balance, end of period	0	260	76
Acquired Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	700
Charge-offs	(500)	(2,700)	$ (4,800)
Balance, end of period	$ 700	$ 700