Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Oct. 31, 2017	Oct. 31, 2016
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	$ 424	$ 467
Interest cost	497	457
Expected return on plan assets	(486)	(476)
Amortization of Prior service costs	1	1
Amortization of Other actuarial loss	287	429
Net periodic benefit cost	723	878
Postretirement Health Plan
Defined Benefit Plans and Other Postretirement Benefit Plans
Service cost	29	30
Interest cost	24	18
Amortization of Prior service costs	(2)	(2)
Amortization of Other actuarial loss	5	6
Net periodic benefit cost	$ 56	$ 52