Schedule of Federal Reserve Bank Stock and Federal Home Loan Bank Stock and Other Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Schedule of Other Securities [Line Items]
Fair Value	$ 66,300	$ 65,200
Federal Reserve Bank Stock and Other Securities [Member]
Schedule of Other Securities [Line Items]
Amortized Cost	57,645	57,075
Gross Unrealized Gains	8,681	8,123
Gross Unrealized Losses	(26)
Fair Value	66,300	65,198
Federal Reserve Bank Stock and Other Securities [Member] | Other securities - non-marketable [Member]
Schedule of Other Securities [Line Items]
Amortized Cost	23,974	23,855
Gross Unrealized Gains	730	964
Gross Unrealized Losses	(26)
Fair Value	24,678	24,819
Federal Reserve Bank Stock and Other Securities [Member] | Other securities - marketable [Member]
Schedule of Other Securities [Line Items]
Amortized Cost	4	5
Gross Unrealized Gains	7,951	7,159
Fair Value	7,955	7,164
Federal Reserve Bank Stock and Other Securities [Member] | FRB and FHLB stock [Member]
Schedule of Other Securities [Line Items]
Amortized Cost	33,667	33,215
Fair Value	$ 33,667	$ 33,215