Equity investees - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Subsidiary, Sale of Stock [Line Items]
Revenues	$ 2,288,432	$ 1,940,008	$ 1,907,672
Net income	154,905	78,615	47,523
Goodwill	431,477	248,890
Impairment on disposal of equity investment		2,700
Equity method investment, nonconsolidated investee or group of investees
Subsidiary, Sale of Stock [Line Items]
Revenues	26,396	19,660	22,286
Net income	7,101	6,231	4,729
Goodwill	4,600	4,600
Equity method investment, nonconsolidated investee or group of investees | Direct operations
Subsidiary, Sale of Stock [Line Items]
Revenues	2,300	700	2,100
Net income	$ 3,500	$ 3,000	$ 1,900