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For credit card hardship program, time range that payment reductions may be granted for modified loans classified as TDRs.

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Loans - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
Loans - Narrative (Details) - USD ($)	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance - purchased credit-impaired loans	$ 3,398,000	$ 3,135,000	$ 3,398,000	$ 3,135,000	$ 3,200,000
Provision expense (credit) for loan and lease losses	900,000	$ 2,600,000	3,500,000	$ 2,400,000
Financing receivable, modifications, recorded investment	$ 236,500,000		$ 236,500,000		234,400,000
Commercial Loan P D Grade One
Accounts, Notes, Loans and Financing Receivable [Line Items]
Lowest expected default probability	1		1
Pass \| Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	1		1
Pass \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	12		12
Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	13		13
Special Mention \| Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	13		13
Unlikely to be Collected Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	16		16
Unlikely to be Collected Financing Receivable \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	16		16
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	14		14
Doubtful
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	15		15
Loan Reassessed \| Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans	$ 1,000,000		$ 1,000,000
Commercial Loan P D Grade Thirteen \| Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans	$ 500,000		$ 500,000
Commercial Loan L G D Grade One \| Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	1		1
Commercial Loan L G D Grade Twelve \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loan grades	12		12
Allowance For TDRs To Recorded Investment Of TDRs
Accounts, Notes, Loans and Financing Receivable [Line Items]
Valuation allowance	$ 28,400,000		$ 28,400,000		$ 37,300,000
Ratio of the allowance for loan losses to loans	12.00%		12.00%		16.00%
Loans Held-For-Sale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, recorded investment	$ 57,900,000		$ 57,900,000		$ 63,200,000
Consumer Portfolio Segment \| Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage			24.00%
Commercial Portfolio Segment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans	20,281,181,000		$ 20,281,181,000		20,271,968,000
Allowance - purchased credit-impaired loans	1,926,000		$ 1,926,000		2,813,000
Commercial Portfolio Segment \| Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forbearance agreements time period			6 months
Commercial Portfolio Segment \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forbearance agreements time period			12 months
Commercial Portfolio Segment \| Finance And Insurance Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans	$ 2,700,000,000		$ 2,700,000,000
Percentage of commercial & industrial loan portfolio	17.00%		17.00%
Percentage contributed in total loan	10.00%		10.00%
Commercial Portfolio Segment \| Loans to Mortgage Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial loans	$ 2,092,366,000		$ 2,092,366,000		$ 2,099,961,000
Percentage of commercial & industrial loan portfolio	13.00%		13.00%
Percentage contributed in total loan	8.00%		8.00%
Commercial Portfolio Segment \| Finance Insurance And Loans To Mortgage Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Percentage of commercial & industrial loan portfolio	30.00%		30.00%
Consumer real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Concentration risk, percentage			23.00%
TDRS maturities			30 years
Consumer real estate \| Heloc And Real Estate Installment Classes
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR, reduction of interest rate by increment, basis points	0.25%		0.25%
Modified interest rate increase	2.00%		2.00%
Consumer real estate \| Heloc And Real Estate Installment Classes \| Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate	1.00%		1.00%
Modified interest rate time period			5 years
Consumer real estate \| Heloc And Real Estate Installment Classes \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate time period			5 years
Credit Card And Other Portfolio Segment \| Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Credit card workout program, granted rate reduction	0.00%		0.00%
Credit Card And Other Portfolio Segment \| Credit card \| Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment reductions, time period			6 months
Credit Card And Other Portfolio Segment \| Credit card \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Payment reductions, time period			1 year
Credit card workout program, term extension			5 years
Permanent mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
TDR, reduction of interest rate by increment, basis points	0.25%		0.25%
Modified interest rate increase	1.00%		1.00%
TDRS maturities			40 years
Permanent mortgage \| Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate	2.00%		2.00%
Modified interest rate time period			5 years
Permanent mortgage \| Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Modified interest rate time period			5 years