Contract balances (Details 2) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Contract assets	$ 136,514		$ 136,514		$ 109,078
Change in contract assets			27,436
Contract liabilities - current	(158,272)		(158,272)		(142,768)
Change in contract liabilities - current			(15,504)
Contract liabilities - noncurrent	(72)		(72)		(19)
Change in contract liabilities - noncurrent			(53)
Net contract liabilities	(21,830)		(21,830)		$ (33,709)
Change in net contract liabilities			11,879
Amounts included in contract liability at the beginning of the period	32,300	$ 22,600	121,700	$ 79,000
Amounts from performance obligations satisfied in prior periods	$ 31,900	$ 20,600	$ 42,900	$ 32,500