Allowance for Loan Losses - Performing and Non Performing Loans (Detail) - USD ($) $ in Thousands		Dec. 31, 2016		Dec. 31, 2015
Performing and non performing loans
Loan receivables		$ 223,976		$ 195,917
Performing
Performing and non performing loans
Loan receivables		221,661		192,780
Nonperforming
Performing and non performing loans
Loan receivables		2,315		3,137
Residential First Mortgages
Performing and non performing loans
Loan receivables		194,007	[1]	164,405	[2]
Residential First Mortgages | Performing
Performing and non performing loans
Loan receivables		191,852	[1]	161,564	[2]
Residential First Mortgages | Nonperforming
Performing and non performing loans
Loan receivables		2,155	[1]	2,841	[2]
Residential Revolving and Junior Mortgages
Performing and non performing loans
Loan receivables		26,425	[3]	26,497	[4]
Residential Revolving and Junior Mortgages | Performing
Performing and non performing loans
Loan receivables		26,265	[3]	26,220	[4]
Residential Revolving and Junior Mortgages | Nonperforming
Performing and non performing loans
Loan receivables		160	[3]	277	[4]
Consumer and Other Loans
Performing and non performing loans
Loan receivables		3,544	[5]	5,015	[6]
Consumer and Other Loans | Performing
Performing and non performing loans
Loan receivables		$ 3,544	[5]	4,996	[6]
Consumer and Other Loans | Nonperforming
Performing and non performing loans
Loan receivables	[6]			$ 19

[1] Residential First Mortgages which have been assigned a risk rating grade of Substandard totaled $3.3 million as of December 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 December 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] No Consumer Loans have been assigned a risk rating grade of Substandard as of December 31, 2016.

[6] No Consumer Loans had been assigned a risk rating grade of Substandard as of December 31, 2015.