Fair Value - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Apr. 30, 2017	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015	Jan. 08, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other-than-temporary impairment losses recognized		$ 0
Marketable Securities			$ 0
Adjustments in contingent consideration		(10,239,000)	141,000	$ (62,000)
PocketSonics
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustments in contingent consideration	$ 0	0
Contingent consideration paid for business acquisitions	2,000,000
Oncura
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustments in contingent consideration		(10,200,000)	100,000
Fair value of contingent consideration obligation	$ 0	$ 0	$ 10,200,000		$ 10,100,000
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long term marketable securities contractual maturities period		1 year
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long term marketable securities contractual maturities period		5 years