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Acquisitions - Additional Information (Detail) $ / shares in Units, $ in Millions		3 Months Ended
	Jul. 31, 2018 USD ($) $ / shares shares	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)
Business Acquisition [Line Items]
Goodwill		$ 413.3	$ 318.6
Counsyl Inc [Member]
Business Acquisition [Line Items]
Business acquisition consideration	$ 407.0
Acquired intangible assets	292.9
Goodwill	$ 94.9
Acquisition costs		6.8
Revenue contributed by acquired entity		19.4
Operating expenses related to acquired entity		$ 33.0
Counsyl Inc [Member] | Measurement Input, Discount Rate [Member]
Business Acquisition [Line Items]
Estimated net cash flows, discount rate	12.5
Counsyl Inc [Member] | Developed Screening Processes [Member]
Business Acquisition [Line Items]
Acquired intangible assets	$ 292.0
Intangible assets estimated useful lives	12 years
Counsyl Inc [Member] | Internally Developed Software [Member]
Business Acquisition [Line Items]
Acquired intangible assets	$ 0.9
Intangible assets estimated useful lives	5 years
Counsyl Inc [Member] | Agreement and Plan of Merger [Member]
Business Acquisition [Line Items]
Effective date of business acquisition	Jul. 31, 2018
Business acquisition consideration	$ 407.0
Cash payment on business acquisition	279.6
Amount of cash consideration deposited in escrow account	$ 5.0
Counsyl Inc [Member] | Agreement and Plan of Merger [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Business acquisition, shares issued | shares	2,994,251
Business acquisition, shares issued, value	$ 127.4
Business acquisition, per share market closing price | $ / shares	$ 42.53

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