Acquisitions - Summary of Preliminary Allocation of Purchase Price to Fair Value of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 03, 2019	Dec. 31, 2018
Assets:
Goodwill	$ 238,826		$ 85,165
SiriusDecisions, Inc [Member]
Assets:
Cash and cash equivalents		$ 7,858
Accounts receivable		19,237
Prepaids and other current assets		3,660
Fixed assets		4,169
Goodwill		154,906
Acquired intangible assets		115,000
Other assets		265
Total assets		305,095
Liabilities:
Accounts payable and accrued liabilities		8,924
Deferred revenue		26,143
Deferred tax liability (2)		22,357
Long-term deferred revenue		1,037
Other long-term liabilities		1,092
Total liabilities		59,553
Net assets acquired		$ 245,542