Revenue - Subscription, Advertising, and Other Revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2020	Sep. 29, 2019	Sep. 27, 2020	Sep. 29, 2019
Disaggregation of Revenue [Line Items]
Total revenues	$ 426,895	$ 428,501	$ 1,274,281	$ 1,303,821
Product and service benchmark | Product concentration risk
Disaggregation of Revenue [Line Items]
As % of total	100.00%	100.00%	100.00%	100.00%
Subscription
Disaggregation of Revenue [Line Items]
Total revenues	$ 300,950	$ 267,302	$ 879,573	$ 808,568
Subscription | Product and service benchmark | Product concentration risk
Disaggregation of Revenue [Line Items]
As % of total	70.50%	62.40%	69.00%	62.00%
Advertising
Disaggregation of Revenue [Line Items]
Total revenues	$ 79,253	$ 113,531	$ 253,150	$ 359,380
Advertising | Product and service benchmark | Product concentration risk
Disaggregation of Revenue [Line Items]
As % of total	18.60%	26.50%	19.90%	27.60%
Other
Disaggregation of Revenue [Line Items]
Total revenues	$ 46,692	$ 47,668	$ 141,558	$ 135,873
Other | Product and service benchmark | Product concentration risk
Disaggregation of Revenue [Line Items]
As % of total	10.90%	11.10%	11.10%	10.40%
Real Estate
Disaggregation of Revenue [Line Items]
Revenue not from contract with customer	$ 7,000	$ 8,000	$ 22,000	$ 23,000