Contract balances (Details 2) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract assets	$ 153,641		$ 153,641		$ 104,239
Change in contract assets			49,402
Contract liabilities - current	(90,031)		(90,031)		(93,901)
Change in contract liabilities - current			3,870
Contract liabilities - noncurrent	(25)		(25)		(135)
Change in contract liabilities - noncurrent			110
Net contract assets	63,585		63,585		$ 10,203
Change in net contract assets			53,382
Amounts included in contract liability at the beginning of the period	22,600	$ 16,900	79,000	$ 68,900
Amounts from performance obligations satisfied in prior periods	$ 20,600	$ 2,600	$ 32,500	$ 5,300