Repurchase Agreements - Additional Information (Detail) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Short-term Debt	$ 15,399,000	$ 11,085,000
Repurchase Agreement Borrowings [Member]
Short-term Debt	15,399,000	10,022,000
US Government Corporations and Agencies Securities
Short-term Debt	$ 18,200,000	$ 18,400,000

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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