Contract balances (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract assets	$ 104,345	$ 109,078	$ 104,239
Change in contract assets	(4,733)	4,839
Contract liabilities - current	(158,603)	(142,768)	(93,901)
Change in contract liabilities - current	(15,835)	(48,867)
Contract liabilities - noncurrent	(52)	(19)	(135)
Change in contract liabilities - noncurrent	(33)	116
Net contract assets (liabilities)	(54,310)	(33,709)	$ 10,203
Change in net contract assets (liabilities)	(20,601)	(43,912)
Amounts included in contract liability at the beginning of the period	138,200	89,000
Amounts from performance obligations satisfied in prior periods	$ 58,800	$ 44,100