Note Allowance for loan losses (Quantitative information by loan class for loans modified as T D R) (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($) loans	Jun. 30, 2016 USD ($) loans	Jun. 30, 2017 USD ($) loans	Jun. 30, 2016 USD ($) loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	788	917	1,557	1,780
Pre-Modification Recorded Investment	$ 35,402	$ 36,044	$ 65,302	$ 81,474
Post Modification Recorded Investment	34,265	35,398	64,907	80,178
Increase (decrease) in the allowance for loan losses as a result of modification	$ 3,298	$ 3,433	$ 6,168	$ 11,522
CRE non-owner occupied
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	4	1	5	3
Pre-Modification Recorded Investment	$ 1,928	$ 197	$ 2,069	$ 6,520
Post Modification Recorded Investment	1,762	197	1,901	6,504
Increase (decrease) in the allowance for loan losses as a result of modification	$ 156	$ 7	$ 145	$ 4,169
CRE owner occupied
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	9	17	12	34
Pre-Modification Recorded Investment	$ 1,546	$ 7,755	$ 2,703	$ 10,850
Post Modification Recorded Investment	1,535	6,625	2,682	9,774
Increase (decrease) in the allowance for loan losses as a result of modification	$ 87	$ 201	$ 143	$ 337
Commercial and industrial
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	15	9	23	15
Pre-Modification Recorded Investment	$ 509	$ 1,057	$ 828	$ 3,586
Post Modification Recorded Investment	535	1,056	2,923	3,583
Increase (decrease) in the allowance for loan losses as a result of modification	$ 49	$ (25)	$ 468	$ (20)
Mortgages
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	179	196	371	404
Pre-Modification Recorded Investment	$ 20,017	$ 18,764	$ 41,085	$ 44,336
Post Modification Recorded Investment	18,819	18,547	38,332	43,021
Increase (decrease) in the allowance for loan losses as a result of modification	$ 1,226	$ 1,398	$ 2,240	$ 3,627
Leasing
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	3		6
Pre-Modification Recorded Investment	$ 122		$ 236
Post Modification Recorded Investment	120		235
Increase (decrease) in the allowance for loan losses as a result of modification	$ 34		$ 66
Credit cards
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	311	409	596	758
Pre-Modification Recorded Investment	$ 2,502	$ 3,775	$ 4,904	$ 7,031
Post Modification Recorded Investment	2,757	4,388	5,400	8,053
Increase (decrease) in the allowance for loan losses as a result of modification	$ 332	$ 651	$ 644	$ 1,227
Home equity lines of credit
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	2	2	2	3
Pre-Modification Recorded Investment	$ 486	$ 208	$ 486	$ 355
Post Modification Recorded Investment	483	251	483	398
Increase (decrease) in the allowance for loan losses as a result of modification	$ 13	$ 139	$ 13	$ 216
Personal
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	250	265	517	531
Pre-Modification Recorded Investment	$ 4,436	$ 4,195	$ 9,034	$ 8,608
Post Modification Recorded Investment	4,443	4,237	9,038	8,648
Increase (decrease) in the allowance for loan losses as a result of modification	$ 998	$ 1,044	$ 2,031	$ 1,931
Auto
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	5	7	7	11
Pre-Modification Recorded Investment	$ 1,965	$ 61	$ 2,001	$ 133
Post Modification Recorded Investment	1,920	64	1,957	140
Increase (decrease) in the allowance for loan losses as a result of modification	$ 348	$ 13	$ 354	$ 25
Other
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	10	11	18	21
Pre-Modification Recorded Investment	$ 1,891	$ 32	$ 1,956	$ 55
Post Modification Recorded Investment	1,891	33	1,956	57
Increase (decrease) in the allowance for loan losses as a result of modification	$ 55	$ 5	$ 64	$ 10