Goodwill and Intangible Assets - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2019 USD ($)
Finite Lived Intangible Assets [Line Items]
Accumulated goodwill impairment losses	$ 0
SiriusDecisions, Inc [Member]
Finite Lived Intangible Assets [Line Items]
Intangible assets acquired	$ 115,000,000