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Securities - Additional Information (Detail)	3 Months Ended	12 Months Ended
Securities - Additional Information (Detail)	Mar. 31, 2016 USD ($) Securities Obligation	Dec. 31, 2015 Securities Obligation
Amortized Cost and Fair Value Debt Securities [Abstract]
Number of U.S. agency and mortgage-backed securities \| Securities	21	52
Number of obligations of state and political subdivisions in an unrealized loss position \| Obligation	6	13
Percentage of investment portfolio	100.00%	100.00%
Weighted-average period of re-pricing of portfolio	4 years 2 months 12 days	4 years 7 months 6 days
Impairment recognized \| $	$ 0