Note Allowance for loan losses (Troubled debt restructurings loan count by type of modification) (Detail) - loans	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	691	440	1,014	854
Extension of Maturity Date	77	44	131	63
Combination Interest Rate Reduction Maturity Date Extension	75	118	117	227
Other Modifications	182	186	355	413
Commercial multi-family
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	0		0
Extension of Maturity Date	1		1
Combination Interest Rate Reduction Maturity Date Extension	0		0
Other Modifications	0		0
CRE non-owner occupied
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	0	4	2	4
Extension of Maturity Date	6	0	11	1
Combination Interest Rate Reduction Maturity Date Extension	0	0	0	0
Other Modifications	0	0	0	0
CRE owner occupied
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	3	1	3	3
Extension of Maturity Date	23	8	42	9
Combination Interest Rate Reduction Maturity Date Extension	0	0	0	0
Other Modifications	0	0	0	0
Commercial and industrial
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	1	0	4	2
Extension of Maturity Date	31	15	50	21
Combination Interest Rate Reduction Maturity Date Extension	0	0	0	0
Other Modifications	0	0	0	0
Construction
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	0		1
Extension of Maturity Date	0		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	26	18	45	32
Extension of Maturity Date	6	15	10	21
Combination Interest Rate Reduction Maturity Date Extension	67	114	103	218
Other Modifications	22	32	45	100
Leasing
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	0	0	0	0
Extension of Maturity Date	0	1	0	1
Combination Interest Rate Reduction Maturity Date Extension	1	2	1	5
Other Modifications	0	0	0	0
Credit cards
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	180	159	311	285
Extension of Maturity Date	0	0	0	0
Combination Interest Rate Reduction Maturity Date Extension	3	0	3	1
Other Modifications	160	152	310	310
Home equity lines of credit
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	0	0	0	0
Extension of Maturity Date	7	1	12	1
Combination Interest Rate Reduction Maturity Date Extension	3	1	7	1
Other Modifications	0	0	0	0
Personal
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	468	250	628	512
Extension of Maturity Date	1	0	3	4
Combination Interest Rate Reduction Maturity Date Extension	0	0	0	0
Other Modifications	0	0	0	1
Auto
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	0	0	0	0
Extension of Maturity Date	2	3	2	4
Combination Interest Rate Reduction Maturity Date Extension	1	1	2	2
Other Modifications	0	1	0	1
Other
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Reduction In Interest Rate	13	8	20	16
Extension of Maturity Date	0	1	0	1
Combination Interest Rate Reduction Maturity Date Extension	0	0	1	0
Other Modifications	0	1	0	1