Revenue (Tables)

9 Months Ended

Sep. 30, 2021

Revenue.

Schedule of revenue by discipline

	Three months ended				Nine months ended
	September 30,				September 30,
	2021		2020		2021		2020
	(in thousands)
Systems	$	126,166	$	70,239	$	307,295	$	229,391
Aftermarket		50,528		40,166		149,449		122,970
Total Revenue	$	176,694	$	110,405	$	456,744	$	352,361

Schedule of revenue by geographic markets

	Three months ended				Nine months ended
	September 30,				September 30,
	2021		2020		2021		2020
	(in thousands)
North America	$	11,847	$	9,022	$	31,560	$	28,598
Asia Pacific		137,870		89,995		357,903		293,427
Europe		26,977		11,388		67,281		30,336
Total Revenue	$	176,694	$	110,405	$	456,744	$	352,361

Schedule of Contract liabilities

	September 30,		December 31,
	2021		2020
	(in thousands)
Contract liabilities	$	58,240	$	23,058

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				Nine months ended
	September 30,				September 30,
	2021		2020		2021		2020
	(in thousands)
Balance, beginning of the period	$	35,518	$	30,416	$	23,058	$	29,251
Deferral of revenue		38,867		4,030		55,011		10,320
Recognition of deferred revenue		(16,145)		(17,477)		(19,829)		(22,602)
Balance, end of the period	$	58,240	$	16,969	$	58,240	$	16,969