Revenue (Tables)

6 Months Ended

Jun. 30, 2018

Revenue

Schedule of revenue by discipline

	Three months ended				Six months ended
	June 30,				June 30,
	2018*		2017		2018*		2017
	(in thousands)				(in thousands)
Systems	$	73,919	$	62,440	$	159,395	$	117,691
Aftermarket		45,414		40,350		82,123		71,992
	$	119,333	$	102,790	$	241,518	$	189,683

Schedule of revenue by geographic markets

	Three months ended				Six months ended
	June 30,				June 30,
	2018*		2017		2018*		2017
	(in thousands)				(in thousands)
North America	$	16,485	$	12,400	$	27,008	$	19,399
Asia		88,471		81,103		186,160		144,347
Europe		14,377		9,287		28,350		25,937
	$	119,333	$	102,790	$	241,518	$	189,683

Schedule of contract assets and contract liabilities

	June 30,		December 31,
	2018		2017
	(in thousands)
Contract assets	$	—	$	—
Contract liabilities	$	15,175	$	18,145

	Three months ended				Six months ended
	June 30,				June 30,
	2018		2017		2018		2017
	(in thousands)
Revenue recognized in the period from:
Amounts included in contract liability at the beginning of the period	$	8,787	$	3,780	$	10,617	$	7,066
Performance obligations satisfied in previous periods	$	—	$	—	$	—	$	—