Summary of significant accounting policies - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2025 USD ($)	Dec. 31, 2025 USD ($) segment	Dec. 31, 2024 USD ($) segment	Dec. 31, 2023 USD ($) segment	Dec. 31, 2022 USD ($)
Property, Plant and Equipment [Line Items]
Number of operating segments | segment		2	2	2
Number of reportable segments | segment		2	2	2
Consumer subscription trail period		7 days
Refund term		30 days
Revenue recognized				$ 270.7	$ 268.3
Advertising expense		$ 80.6	$ 94.9	82.5
Amortization period (in years)	4 years	4 years
Renewal term (in months)	18 months	18 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Property, Plant and Equipment [Line Items]
Revenue, remaining performance obligation, period (in months)	12 months	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01
Property, Plant and Equipment [Line Items]
Revenue, remaining performance obligation, period (in months)
Minimum
Property, Plant and Equipment [Line Items]
Consumer subscriptions		1 month
Maximum
Property, Plant and Equipment [Line Items]
Consumer subscriptions		1 year
Equipment
Property, Plant and Equipment [Line Items]
Equipment useful lives (in years)	3 years	3 years
Computers and equipment
Property, Plant and Equipment [Line Items]
Equipment useful lives (in years)	3 years	3 years
Purchased software
Property, Plant and Equipment [Line Items]
Equipment useful lives (in years)	3 years	3 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Equipment useful lives (in years)	5 years	5 years
Breakage
Property, Plant and Equipment [Line Items]
Revenue recognized	$ 0.0	$ 2.7	$ 0.0	$ 0.0
Previously satisfied performance obligations		$ 2.5
Consumer Single Course Purchases | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Property, Plant and Equipment [Line Items]
Revenue, remaining performance obligation, period (in months)	4 months	4 months
Internal use software
Property, Plant and Equipment [Line Items]
Estimated useful lives (in years)	3 years	3 years
Content assets
Property, Plant and Equipment [Line Items]
Estimated useful lives (in years)	2 years	2 years