Reconciliations of Equity - Reconciliations of Total Equity (Parenthetical) (Detail) - $ / shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Number of shares of common stock issued under stock option plan	38,706	77,474
Number of common stock shares purchased	900	6,107
Common stock	$ 0.25	$ 0.23
Common Stock [Member]
Number of shares of common stock issued under stock option plan	38,706	77,474
Additional Paid-in Capital [Member]
Number of shares of common stock issued under stock option plan	38,706	77,474
Treasury Stock [Member]
Number of common stock shares purchased	900	6,107
Retained Earnings [Member]
Common stock	$ 0.25	$ 0.23