Reconciliations of Equity - Reconciliations of Total Equity (Parenthetical) (Detail) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Number of shares of common stock issued under stock option plan	13,256	5,032	56,385	85,394
Number of common stock shares purchased	73,821	16,833	144,457	156,524
Common stock	$ 0.25	$ 0.23	$ 0.75	$ 0.70
Common Stock [Member]
Number of shares of common stock issued under stock option plan	13,256	5,032	56,385	85,394
Additional Paid-in Capital [Member]
Number of shares of common stock issued under stock option plan	13,256	5,032	56,385	85,394
Treasury Stock [Member]
Number of common stock shares purchased	73,821	16,833	144,457	156,524
Retained Earnings [Member]
Common stock	$ 0.25	$ 0.23	$ 0.75	$ 0.70