Note Allowance for loan losses (Quantitative information by loan class for loans modified as T D R) (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2017 USD ($) loans	Mar. 31, 2016 USD ($) loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	769	863
Pre-Modification Recorded Investment	$ 29,900	$ 45,430
Post Modification Recorded Investment	30,642	44,780
Increase (decrease) in the allowance for loan losses as a result of modification	$ 2,870	$ 8,089
CRE non-owner occupied
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	1	2
Pre-Modification Recorded Investment	$ 141	$ 6,323
Post Modification Recorded Investment	139	6,307
Increase (decrease) in the allowance for loan losses as a result of modification	$ (11)	$ 4,163
CRE owner occupied
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	3	17
Pre-Modification Recorded Investment	$ 1,157	$ 3,095
Post Modification Recorded Investment	1,147	3,149
Increase (decrease) in the allowance for loan losses as a result of modification	$ 56	$ 136
Commercial and industrial
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	8	6
Pre-Modification Recorded Investment	$ 319	$ 2,529
Post Modification Recorded Investment	2,388	2,527
Increase (decrease) in the allowance for loan losses as a result of modification	$ 419	$ 5
Mortgages
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	192	208
Pre-Modification Recorded Investment	$ 21,068	$ 25,572
Post Modification Recorded Investment	19,513	24,474
Increase (decrease) in the allowance for loan losses as a result of modification	$ 1,014	$ 2,229
Leasing
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	3
Pre-Modification Recorded Investment	$ 114
Post Modification Recorded Investment	115
Increase (decrease) in the allowance for loan losses as a result of modification	$ 32
Credit cards
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	285	349
Pre-Modification Recorded Investment	$ 2,402	$ 3,256
Post Modification Recorded Investment	2,643	3,665
Increase (decrease) in the allowance for loan losses as a result of modification	$ 312	$ 576
Home equity lines of credit
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans		1
Pre-Modification Recorded Investment		$ 147
Post Modification Recorded Investment		147
Increase (decrease) in the allowance for loan losses as a result of modification		$ 77
Personal
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	267	266
Pre-Modification Recorded Investment	$ 4,598	$ 4,413
Post Modification Recorded Investment	4,595	4,411
Increase (decrease) in the allowance for loan losses as a result of modification	$ 1,033	$ 887
Auto
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	2	4
Pre-Modification Recorded Investment	$ 36	$ 72
Post Modification Recorded Investment	37	76
Increase (decrease) in the allowance for loan losses as a result of modification	$ 6	$ 12
Other
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	8	10
Pre-Modification Recorded Investment	$ 65	$ 23
Post Modification Recorded Investment	65	24
Increase (decrease) in the allowance for loan losses as a result of modification	$ 9	$ 4