Interim Consolidated Financial Statements - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Jan. 03, 2019	Jan. 01, 2019
Summary Of Significant Accounting Policy [Line Items]
Operating lease right-of-use assets	$ 73,167	$ 73,167
Operating lease liabilities	82,144	$ 82,144
Lease package practical expedients		true
Option to extend description		Some of the Company’s leases include options to extend or terminate the lease. When determining the lease term, these options are included in the measurement and recognition of the Company’s ROU assets and lease liabilities when it is reasonably certain that the Company will exercise the option.
Topic 842 [Member]
Summary Of Significant Accounting Policy [Line Items]
Operating lease right-of-use assets				$ 53,300
Operating lease liabilities				60,800
Topic 842 [Member] | Effect of Adoption [Member]
Summary Of Significant Accounting Policy [Line Items]
Deferred rent				$ 7,500
Topic 842 [Member] | SiriusDecisions, Inc [Member]
Summary Of Significant Accounting Policy [Line Items]
Operating lease right-of-use assets			$ 10,400
Operating lease liabilities			$ 10,400
Topic 842 [Member] | SiriusDecisions, Inc [Member] | Facility Lease [Member]
Summary Of Significant Accounting Policy [Line Items]
Operating lease right-of-use asset impairments	$ 300	$ 300