Note Allowance for loan losses (T D R that subsequently defaulted) (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) loans	Mar. 31, 2017 USD ($) loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	102	214
Recorded investment as of first default date | $	$ 4,961	$ 7,340
CRE non-owner occupied
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans		1
Recorded investment as of first default date | $		$ 262
CRE owner occupied
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	2	1
Recorded investment as of first default date | $	$ 86	$ 267
Commercial and industrial
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	5	2
Recorded investment as of first default date | $	$ 72	$ 544
Mortgages
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	17	36
Recorded investment as of first default date | $	$ 2,572	$ 3,695
Leasing
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans		1
Recorded investment as of first default date | $		$ 45
Credit cards
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	48	128
Recorded investment as of first default date | $	$ 1,342	$ 1,349
Home equity lines of credit
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans		1
Recorded investment as of first default date | $		$ 97
Personal
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	30	42
Recorded investment as of first default date | $	$ 889	$ 1,024
Auto
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans		2
Recorded investment as of first default date | $		$ 57