Note Allowance for loan losses (T D R that subsequently defaulted) (Detail) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) loans	Sep. 30, 2016 USD ($) loans	Sep. 30, 2017 USD ($) loans	Sep. 30, 2016 USD ($) loans
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	252	209	538	478
Recorded investment as of first default date | $	$ 6,705	$ 8,720	$ 19,015	$ 23,304
CRE non-owner occupied
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	0	0	2	2
Recorded investment as of first default date | $	$ 0	$ 0	$ 457	$ 327
CRE owner occupied
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	0	3	3	10
Recorded investment as of first default date | $	$ 0	$ 773	$ 1,749	$ 3,276
Commercial and industrial
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	1	3	4	5
Recorded investment as of first default date | $	$ 36	$ 758	$ 601	$ 785
Mortgages
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	48	52	110	132
Recorded investment as of first default date | $	$ 4,216	$ 5,409	$ 10,112	$ 14,132
Leasing
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans		0		4
Recorded investment as of first default date | $		$ 0		$ 29
Credit cards
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	135	109	274	221
Recorded investment as of first default date | $	$ 1,212	$ 1,084	$ 2,661	$ 2,259
Home equity lines of credit
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	0		1
Recorded investment as of first default date | $	$ 0		$ 97
Personal
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	67	34	138	93
Recorded investment as of first default date | $	$ 1,222	$ 623	$ 3,230	$ 2,375
Auto
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	1	3	5	6
Recorded investment as of first default date | $	$ 19	$ 63	$ 99	$ 111
Other
Troubled Debt Restructuring, Debtor, Current Period [Line Items]
Loan count | loans	0	5	1	5
Recorded investment as of first default date | $	$ 0	$ 10	$ 9	$ 10