Reconciliations of Equity - Reconciliations of Total Equity (Parenthetical) (Detail) - $ / shares	3 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018
Number of shares of common stock issued under stock option plan	4,423	38,706	2,888	77,474
Number of common stock shares purchased	69,736	900	133,584	6,107
Common stock	$ 0.25	$ 0.25	$ 0.23	$ 0.23
Common Stock [Member]
Number of shares of common stock issued under stock option plan	4,423	38,706	2,888	77,474
Additional Paid-in Capital [Member]
Number of shares of common stock issued under stock option plan	4,423	38,706	2,888	77,474
Treasury Stock [Member]
Number of common stock shares purchased	69,736	900	133,584	6,107
Retained Earnings [Member]
Common stock	$ 0.25	$ 0.25	$ 0.23	$ 0.23