Acquisition-Related Amortization and Remeasurement - Components of Acquisition-Related Amortization and Remeasurement (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Acquisition Related Amortization And Remeasurement [Abstract]
Changes in fair value of contingent consideration	$ 22,270	$ 1,580	$ 28,140	$ 2,689
Amortization of acquired intangibles	1,338	429	3,733	802
Total	$ 23,608	$ 2,009	$ 31,873	$ 3,491

The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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