Revenue (Tables)

6 Months Ended

Jun. 30, 2020

Revenue.

Schedule of revenue by discipline

	Three months ended				Six months ended
	June 30,				June 30,
	2020		2019		2020		2019
	(in thousands)
Systems	$	76,815	$	37,224	$	159,152	$	94,316
Aftermarket		46,150		37,081		82,804		71,466
	$	122,965	$	74,305	$	241,956	$	165,782

Schedule of revenue by geographic markets

	Three months ended				Six months ended
	June 30,				June 30,
	2020		2019		2020		2019
	(in thousands)
North America	$	8,915	$	9,380	$	19,576	$	20,988
Asia Pacific		106,604		49,717		203,432		112,643
Europe		7,446		15,208		18,948		32,151
	$	122,965	$	74,305	$	241,956	$	165,782

Schedule of Contract liabilities

	June 30,		December 31,
	2020		2019
	(in thousands)
Contract liabilities	$	30,417	$	29,251

Contract liabilities are reflected as deferred revenue on the consolidated balance sheet and relate to payments invoiced or received in advance of completion of performance obligations under a contract. Contract liabilities are recognized as revenue upon the fulfillment of performance obligations.

	Three months ended				Six months ended
	June 30,				June 30,
	2020		2019		2020		2019
	(in thousands)
Balance, beginning of the period	$	34,106	$	20,481	$	29,251	$	22,584
Deferral of revenue		6,248		3,943		10,724		6,225
Recognition of deferred revenue		(9,937)		(10,344)		(9,558)		(14,729)
Balance, ending of the period	$	30,417	$	14,080	$	30,417	$	14,080