Allowance for Loan Losses and Credit Quality of Loans, Allowance for Loan Losses by Portfolio Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	$ 69,500	$ 65,200	$ 63,018
Charge-offs	(34,128)	(33,087)	(29,299)
Recoveries	8,305	6,399	6,050
Provision	28,828	30,988	25,431
Balance, end of period	72,505	69,500	65,200
Commercial Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	27,606	25,444	25,545
Charge-offs	(3,463)	(4,169)	(4,592)
Recoveries	1,178	1,077	1,887
Provision	7,438	5,254	2,604
Balance, end of period	32,759	27,606	25,444
Consumer Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	36,830	33,375	29,253
Charge-offs	(29,752)	(27,072)	(23,364)
Recoveries	6,821	5,142	3,870
Provision	23,279	25,385	23,616
Balance, end of period	37,178	36,830	33,375
Residential Real Estate [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	5,064	6,381	7,960
Charge-offs	(913)	(1,846)	(1,343)
Recoveries	306	180	293
Provision	(1,889)	349	(529)
Balance, end of period	2,568	5,064	6,381
Unallocated [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	0	0	260
Charge-offs	0	0	0
Recoveries	0	0	0
Provision	0	0	(260)
Balance, end of period	0	0	0
Acquired Loans [Member]
Changes in allowance for loan losses by portfolio segment [Roll Forward]
Balance, beginning of period	0
Charge-offs	(100)	(700)	$ (500)
Balance, end of period	$ 0	$ 0