Contract balances (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Contract assets	$ 109,078	$ 104,239	$ 109,540
Change in contract assets	4,839	(5,301)
Contract liabilities - current	(142,768)	(93,901)	(84,123)
Change in contract liabilities - current	(48,867)	(9,778)
Contract liabilities - noncurrent	(19)	(135)	0
Change in contract liabilities - noncurrent	116	(135)
Net contract assets (liabilities)	(33,709)	10,203	$ 25,417
Change in net contract assets	(43,912)	(15,214)
Amounts included in contract liability at the beginning of the period	89,000	78,600
Amounts from performance obligations satisfied in prior periods	$ 44,100	$ 36,700