Employee and Director Stock Plans - Options Outstanding and Exercisable (Detail)	Jan. 31, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Vested and Exercisable, Number of Shares | shares	218,800
Options Vested and Exercisable, Weighted average exercise price (in dollars per share)	$ 40.49
$28.56 - $36.44
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of per-share exercise prices, Lower Limit	28.56
Range of per-share exercise prices, Upper Limit	$ 36.44
Options Vested and Exercisable, Number of Shares | shares	32,600
Options Vested and Exercisable, Weighted average exercise price (in dollars per share)	$ 34.23
$38.55 - $38.55
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of per-share exercise prices, Lower Limit	38.55
Range of per-share exercise prices, Upper Limit	$ 38.55
Options Vested and Exercisable, Number of Shares | shares	1,800
Options Vested and Exercisable, Weighted average exercise price (in dollars per share)	$ 38.55
$41.62 - $41.62
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of per-share exercise prices, Lower Limit	41.62
Range of per-share exercise prices, Upper Limit	$ 41.62
Options Vested and Exercisable, Number of Shares | shares	184,400
Options Vested and Exercisable, Weighted average exercise price (in dollars per share)	$ 41.62