Reconciliations of Equity - Reconciliations of Total Equity (Parenthetical) (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Number of shares of common stock issued under stock option plan	5,786	2,747
Number of common stock shares purchased	8,300	89,225
Common stock	$ 0.305	$ 0.275
Common Stock [Member]
Number of shares of common stock issued under stock option plan	5,786	2,747
Additional Paid-in Capital [Member]
Number of shares of common stock issued under stock option plan	5,786	2,747
Common Treasury Stock [Member]
Number of common stock shares purchased	8,300	89,225
Retained Earnings [Member]
Common stock	$ 0.305	$ 0.275