Note Allowance for loan losses (T D R that subsequently defaulted) (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($) loans	Jun. 30, 2017 USD ($) loans	Jun. 30, 2018 USD ($) loans	Jun. 30, 2017 USD ($) loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	161	119	225	204
Recorded investment as of first default date | $	$ 3,420	$ 5,810	$ 8,092	$ 11,588
CRE non-owner occupied
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	1	1	1	2
Recorded investment as of first default date | $	$ 17	$ 195	$ 17	$ 457
CRE owner occupied
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	1	2	3	3
Recorded investment as of first default date | $	$ 50	$ 1,483	$ 136	$ 1,749
Commercial and industrial
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	1	1	6	3
Recorded investment as of first default date | $	$ 4	$ 21	$ 76	$ 565
Mortgages
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	15	30	32	62
Recorded investment as of first default date | $	$ 1,668	$ 2,542	$ 4,240	$ 5,896
Credit cards
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	102	27	125	46
Recorded investment as of first default date | $	$ 1,073	$ 349	$ 2,155	$ 648
Home equity lines of credit
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	0	1	0	2
Recorded investment as of first default date | $	$ 0	$ 97	$ 0	$ 140
Personal
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	38	55	55	82
Recorded investment as of first default date | $	$ 578	$ 1,095	$ 1,438	$ 2,070
Auto
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	1	1	1	3
Recorded investment as of first default date | $	$ 22	$ 19	$ 22	$ 54
Other
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	2	1	2	1
Recorded investment as of first default date | $	$ 8	$ 9	$ 8	$ 9