Contract balances (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Contract assets	$ 135,958		$ 135,958		$ 109,078
Change in contract assets			26,880
Contract liabilities - current	(158,923)		(158,923)		(142,768)
Change in contract liabilities - current			(16,155)
Contract liabilities - noncurrent	(62)		(62)		(19)
Change in contract liabilities - noncurrent			(43)
Net contract liabilities	(23,027)		(23,027)		$ (33,709)
Change in net contract liabilities			10,682
Amounts included in contract liability at the beginning of the period	15,600	$ 7,500	137,300	$ 86,500
Amounts from performance obligations satisfied in prior periods	$ 34,700	$ 21,800	$ 58,800	$ 40,300