Investments and other assets - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Equity investments, impairment loss	$ 9.2
Gain on other equity investment		$ 5.9
Other Equity Investments
Schedule of Equity Method Investments [Line Items]
Gain on other equity investment		$ 5.9