Revenue (Tables)

6 Months Ended

Jun. 30, 2021

Revenue.

Schedule of revenue by discipline

	Three months ended				Six months ended
	June 30,				June 30,
	2021		2020		2021		2020
	(in thousands)
Systems	$	100,138	$	76,815	$	181,129	$	159,152
Aftermarket		47,136		46,150		98,921		82,804
Total Revenue	$	147,274	$	122,965	$	280,050	$	241,956

Schedule of revenue by geographic markets

	Three months ended				Six months ended
	June 30,				June 30,
	2021		2020		2021		2020
	(in thousands)
North America	$	10,204	$	8,915	$	19,712	$	19,576
Asia Pacific		116,642		106,604		220,033		203,432
Europe		20,428		7,446		40,305		18,948
Total Revenue	$	147,274	$	122,965	$	280,050	$	241,956

Schedule of Contract liabilities

	June 30,		December 31,
	2021		2020
	(in thousands)
Contract liabilities	$	35,518	$	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				Six months ended
	June 30,				June 30,
	2021		2020		2021		2020
	(in thousands)
Balance, beginning of the period	$	22,142	$	34,106	$	23,058	$	29,251
Deferral of revenue		21,893		6,248		30,117		10,724
Recognition of deferred revenue		(8,517)		(9,937)		(17,657)		(9,558)
Balance, end of the period	$	35,518	$	30,417	$	35,518	$	30,417