Commitment and Contingencies - Narrative (Details) $ in Millions		3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
	Jul. 01, 2020 USD ($)	Jun. 30, 2020 USD ($) Displays	Jun. 30, 2020 USD ($) Displays	Dec. 31, 2020	Dec. 31, 2019 USD ($)
Subsequent event
Other Commitments [Line Items]
Equipment Deployment Costs Percentage	30.00%
Standalone letters of credit and sublimit to revolving credit facility
Other Commitments [Line Items]
Letters of credit outstanding, amount | $		$ 72.6	$ 72.6
Surety Bond
Other Commitments [Line Items]
Surety bonds outstanding | $		$ 161.5	161.5
MTA Agreement | Subsequent event
Other Commitments [Line Items]
Revenue share percentage				65.00%
MTA equipment deployment costs
Other Commitments [Line Items]
Deployment costs incurred | $			$ 28.3		$ 124.2
Metropolitan Transportation Authority ("MTA") | Subsequent event
Other Commitments [Line Items]
Equipment Deployment Costs Percentage	70.00%
Maximum | MTA equipment deployment costs | Subsequent event
Other Commitments [Line Items]
Deployment costs incurred | $	$ 143.0
MTA digital advertising screens on subway and train platforms
Other Commitments [Line Items]
Number of displays		8,565	8,565
MTA smaller-format digital advertising screens rolling stock
Other Commitments [Line Items]
Number of displays		37,716	37,716
MTA communication displays
Other Commitments [Line Items]
Number of displays		7,829	7,829
MTA displays installed
Other Commitments [Line Items]
Number of displays		5,350	5,350
Number of display additions		97	773