Acquisitions - Summary of Allocation of Purchase Price to Fair Value of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 03, 2019	Dec. 31, 2018	Jul. 06, 2018	Dec. 31, 2017
Assets:
Goodwill	$ 243,895		$ 85,165		$ 76,169
SiriusDecisions, Inc [Member]
Assets:
Cash and cash equivalents		$ 7,858
Accounts receivable		19,237
Prepaids and other current assets		3,660
Property and equipment		4,169
Goodwill		158,569
Intangible assets		115,000
Other assets		418
Total assets		308,911
Liabilities:
Accounts payable and other current liabilities		8,924
Deferred revenue		26,143
Deferred tax liability		26,226
Long-term deferred revenue		1,037
Other long-term liabilities		1,039
Total liabilities		63,369
Net assets acquired		$ 245,542
FeedbackNow [Member]
Assets:
Cash and cash equivalents				$ 463
Accounts receivable				738
Prepaids and other current assets				487
Goodwill				9,513
Intangible assets				4,780
Other assets				75
Total assets				16,056
Liabilities:
Accounts payable and other current liabilities				837
Contract liabilities				298
Deferred tax liability				825
Total liabilities				1,960
Net assets acquired				$ 14,096