Property and Equipment, net - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Property, Plant and Equipment [Line Items]
Amortization and depreciation expense related to property and equipment other than website development costs	$ 7.3	$ 6.1	$ 26.2	$ 18.5
Capitalization of website development costs	15.0	10.8	42.9	31.1
Amortization of website development costs and intangible assets included in technology and development	12.8	11.1	37.7	33.1
Technology and development \| Software Development
Property, Plant and Equipment [Line Items]
Amortization of website development costs and intangible assets included in technology and development	$ 6.2	$ 4.8	$ 17.6	$ 11.8

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.

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Additions made to capitalized computer software costs during the period.

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Amount of expense charged against earnings to allocate the cost of tangible and intangible assets over their remaining economic lives, classified as other.

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