Schedule II Valuation of Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balances at beginning of period	$ 5,144	$ 3,585	$ 3,069
Additions — Charged to expense	732	1,904	1,954
Deductions - written off	(1,247)	(345)	(1,438)
Balances at end of period	4,629	5,144	3,585
Inventory Valuation Reserve [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balances at beginning of period	15,083	13,269	12,259
Additions — Charged to expense	4,608	4,950	3,017
Deductions - written off	(5,369)	(3,136)	(2,007)
Balances at end of period	14,322	15,083	13,269
Valuation Allowance of Deferred Tax Assets [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balances at beginning of period	37,992	39,922	37,409
Additions — Charged to expense	2,004	2,614	8,111
Deductions - written off	(1,433)	(4,544)	(5,598)
Balances at end of period	$ 38,563	$ 37,992	$ 39,922