Annual report pursuant to Section 13 and 15(d)

Commitments (Details)

Commitments (Details) - USD ($)
$ in Thousands
12 Months Ended
Jul. 31, 2018
Jul. 31, 2017
Jul. 31, 2016
Commitments (Details) [Line Items]      
Description Of Operating Leases The Company leases equipment, office and laboratory space underseveral non-cancellable operating leases that expire through June 2028. Certain leases include renewal options and rent escalationclauses. An entity owned by certain executive officers/directors of the Company owns the building that the Company leases as itsmain facility for clinical laboratory operations and certain research operations. In addition to the minimum annual rentals ofspace, the lease is subject to annual increases, based on the consumer price index. Annual increases are limited to 3% per year    
Maximum Annual Rental Increase Percentage 3.00%    
Rent expense Including Real Estate Taxes $ 1,798 $ 1,752 $ 1,704
Amount of Real Estate Tax Abatement Received     61
Operating Leases, Rent Expense 4,398 $ 4,658 $ 4,572
Operating Leases, Rent Expense, Sublease Rentals $ 323    
Agreement Renew Period 2 years    
Other Commitment, Due in Next Twelve Months $ 2,498    
Maximum [Member]      
Commitments (Details) [Line Items]      
Lease Expiration Month and Year June 2028