Note Allowance for loan losses (Troubled debt restructurings loan count by type of modification) (Detail) - loans	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	414	489
Extension of Maturity Date	19	19
Combination Interest Rate Reduction Maturity Date Extension	109	126
Other Modifications	227	229
CRE non-owner occupied
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	0	1
Extension of Maturity Date	1	1
Combination Interest Rate Reduction Maturity Date Extension	0	0
Other Modifications	0	0
CRE owner occupied
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	2	16
Extension of Maturity Date	1	1
Combination Interest Rate Reduction Maturity Date Extension	0	0
Other Modifications	0	0
Commercial and industrial
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	2	6
Extension of Maturity Date	6	0
Combination Interest Rate Reduction Maturity Date Extension	0	0
Other Modifications	0	0
Mortgages
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	14	20
Extension of Maturity Date	6	10
Combination Interest Rate Reduction Maturity Date Extension	104	123
Other Modifications	68	55
Leasing
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	0
Extension of Maturity Date	0
Combination Interest Rate Reduction Maturity Date Extension	3
Other Modifications	0
Credit cards
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	126	175
Extension of Maturity Date	0	0
Combination Interest Rate Reduction Maturity Date Extension	1	0
Other Modifications	158	174
Home equity lines of credit
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate		0
Extension of Maturity Date		0
Combination Interest Rate Reduction Maturity Date Extension		1
Other Modifications		0
Personal
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	262	261
Extension of Maturity Date	4	5
Combination Interest Rate Reduction Maturity Date Extension	0	0
Other Modifications	1	0
Auto
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	0	0
Extension of Maturity Date	1	2
Combination Interest Rate Reduction Maturity Date Extension	1	2
Other Modifications	0	0
Other
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	8	10
Extension of Maturity Date	0	0
Combination Interest Rate Reduction Maturity Date Extension	0	0
Other Modifications	0	0