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Interim Consolidated Financial Statements - Additional Information (Detail) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2019
Jan. 03, 2019
Jan. 01, 2019
Summary Of Significant Accounting Policy [Line Items]      
Operating lease right-of-use assets $ 71,529    
Operating lease liabilities $ 80,247    
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] | Restatement Adjustment      
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