Summary of Significant Accounting Policies - Computation of Weighted Average Number of Common Shares Outstanding for Basic and Diluted Earnings Per Share (Detail) - shares	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Weighted Average Number of Shares Outstanding, Diluted [Abstract]
Weighted average common shares	2,980,602	2,980,602	2,980,602
Average treasury shares	(238,252)	(238,306)	(238,360)
Total weighted average common shares outstanding basic and diluted	2,742,350	2,742,296	2,742,242

This element represents the weighted average total number of shares issued throughout the period including the first (beginning balance outstanding) and last (ending balance outstanding) day of the period before considering any reductions (for instance, shares held in treasury) to arrive at the weighted average number of shares outstanding. Weighted average relates to the portion of time within a reporting period that common shares have been issued and outstanding to the total time in that period. Such concept is used in determining the weighted average number of shares outstanding for purposes of calculating earnings per share (basic).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=121326447&loc=d3e1448-109256

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=121326447&loc=d3e2646-109256

Name:	us-gaap_WeightedAverageNumberOfSharesIssuedBasic
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration