Allowance for Loan Losses - Performing and Non Performing Loans (Parenthetical) (Detail) - USD ($) $ in Thousands	Mar. 31, 2016		Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Risk rating grade totaled	$ 199,107		$ 195,917
Residential First Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Risk rating grade totaled	167,478	[1]	164,405	[2]
Residential Revolving and Junior Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Risk rating grade totaled	26,592	[3]	26,497	[4]
Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Risk rating grade totaled	5,037	[5]	5,015	[6]
Substandard | Residential First Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Risk rating grade totaled	4,000		3,900
Substandard | Residential Revolving and Junior Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Risk rating grade totaled	1,100		372
Substandard | Consumer and Other Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Risk rating grade totaled	$ 24		$ 0

[1] Residential First Mortgages which have been assigned a risk rating grade of Substandard totaled $4.0 million as of March 31, 2016.

[2] Residential First Mortgages which have been assigned a risk rating grade of Substandard totaled $3.9 million as of December 31, 2015.

[3] Residential Revolving and Junior Mortgages which have been assigned a risk rating grade of Substandard totaled $1.1 million as of March 31, 2016.

[4] Residential Revolving and Junior Mortgages which have been assigned a risk rating grade of Substandard totaled $372 thousand as of December 31, 2015.

[5] Consumer Loans which have been assigned a risk rating grade of Substandard were $24 thousand as of March 31, 2016.

[6] No consumer Loans which have been assigned a risk rating grade of Substandard as of December 31, 2015.