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, 2019 USD ($) loans	Mar. 31, 2018 USD ($) loans
Troubled Debt Restructuring
Loan count | loans	578	592
Pre-Modification Recorded Investment	$ 32,430	$ 60,666
Post Modification Recorded Investment	30,694	58,441
Increase (decrease) in the allowance for loan losses as a result of modification	$ 2,059	$ 9,539
CRE non-owner occupied
Troubled Debt Restructuring
Loan count | loans	1	7
Pre-Modification Recorded Investment	$ 314	$ 22,986
Post Modification Recorded Investment	311	22,923
Increase (decrease) in the allowance for loan losses as a result of modification	$ 18	$ 6,800
CRE owner occupied
Troubled Debt Restructuring
Loan count | loans	10	19
Pre-Modification Recorded Investment	$ 2,019	$ 4,974
Post Modification Recorded Investment	1,973	4,269
Increase (decrease) in the allowance for loan losses as a result of modification	$ 19	$ 138
Commercial and industrial
Troubled Debt Restructuring
Loan count | loans	16	22
Pre-Modification Recorded Investment	$ 3,943	$ 11,069
Post Modification Recorded Investment	4,479	10,523
Increase (decrease) in the allowance for loan losses as a result of modification	$ 314	$ (110)
Construction
Troubled Debt Restructuring
Loan count | loans		1
Pre-Modification Recorded Investment		$ 4,210
Post Modification Recorded Investment		4,293
Increase (decrease) in the allowance for loan losses as a result of modification		$ 474
Mortgages
Troubled Debt Restructuring
Loan count | loans	190	82
Pre-Modification Recorded Investment	$ 20,732	$ 10,273
Post Modification Recorded Investment	18,591	8,919
Increase (decrease) in the allowance for loan losses as a result of modification	$ 671	$ 457
Credit cards
Troubled Debt Restructuring
Loan count | loans	189	281
Pre-Modification Recorded Investment	$ 1,543	$ 2,926
Post Modification Recorded Investment	1,530	3,301
Increase (decrease) in the allowance for loan losses as a result of modification	$ 171	$ 454
Home equity lines of credit
Troubled Debt Restructuring
Loan count | loans	10	9
Pre-Modification Recorded Investment	$ 694	$ 865
Post Modification Recorded Investment	621	856
Increase (decrease) in the allowance for loan losses as a result of modification	$ 55	$ 267
Personal Loan
Troubled Debt Restructuring
Loan count | loans	154	162
Pre-Modification Recorded Investment	$ 3,147	$ 3,072
Post Modification Recorded Investment	3,153	3,070
Increase (decrease) in the allowance for loan losses as a result of modification	$ 805	$ 1,010
Auto Loan
Troubled Debt Restructuring
Loan count | loans	2	1
Pre-Modification Recorded Investment	$ 25	$ 134
Post Modification Recorded Investment	23	132
Increase (decrease) in the allowance for loan losses as a result of modification	$ 4	$ 23
Other
Troubled Debt Restructuring
Loan count | loans	6	8
Pre-Modification Recorded Investment	$ 13	$ 157
Post Modification Recorded Investment	13	155
Increase (decrease) in the allowance for loan losses as a result of modification	$ 2	$ 26