Subsequent Events - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended	6 Months Ended		14 Months Ended
	May 31, 2017	Sep. 07, 2017	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017
Subsequent Event [Line Items]
Stock repurchased during period, shares			758,508		1,163,597
Stock repurchased during period, cash			$ 38,720	$ 20,183	$ 58,900
Amount available under stock repurchase program			$ 47,800		$ 47,800
Subsequent Event [Member]
Subsequent Event [Line Items]
Stock repurchased during period, shares		59,143
Stock repurchased during period, cash		$ 2,700
Amount available under stock repurchase program		$ 45,100
Stock Repurchase Program $50.0 Million Authorization [Member]
Subsequent Event [Line Items]
Stock repurchase program, expiration date	Jun. 30, 2018