Past Due Loans, Allowances For Credit Losses, Impaired Loans, and TDRs (Detail) - Credit Quality Indicators by Class, Excluding Covered Loans (Continued) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Home equity
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	$ 543,185	$ 427,020
1-4 family mortgages
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	291,463	275,992
Installment
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	76,032	44,827
Total consumer loans
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	910,680	747,839
Performing | Home equity
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	536,895	420,156
Performing | 1-4 family mortgages
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	288,522	270,794
Performing | Installment
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	75,989	42,751
Performing | Total consumer loans
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	901,406	733,701
Non-accrual | Home equity
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	6,290	6,864
Non-accrual | 1-4 family mortgages
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	2,941	5,198
Non-accrual | Installment
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	43	2,076
Non-accrual | Total consumer loans
Credit Quality Indicators by Class, Excluding Covered Loans [Line Items]
Credit Quality Indicators by Class	$ 9,274	$ 14,138