Contract balances (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract assets	$ 163,437		$ 163,437		$ 104,239
Change in contract assets			59,198
Contract liabilities - current	(120,207)		(120,207)		(93,901)
Change in contract liabilities - current			(26,306)
Contract liabilities - noncurrent	(25)		(25)		(135)
Change in contract liabilities - noncurrent			110
Net contract assets	43,205		43,205		$ 10,203
Change in net contract assets			33,002
Amounts included in contract liability at the beginning of the period	7,500	$ 10,300	86,500	$ 79,200
Amounts from performance obligations satisfied in prior periods	$ 21,800	$ (8,700)	$ 40,300	$ (3,700)