Contract balances (Details 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Contract assets	$ 121,321		$ 109,078
Change in contract assets	12,243
Contract liabilities - current	(153,230)		(142,768)
Change in contract liabilities - current	(10,462)
Contract liabilities - noncurrent	(81)		(19)
Change in contract liabilities - noncurrent	(62)
Net contract liabilities	(31,990)		$ (33,709)
Change in net contract liabilities	1,719
Amounts included in contract liability at the beginning of the period	89,400	$ 56,400
Amounts from performance obligations satisfied in prior periods	$ 19,500	$ 18,700