Revenue (Tables)

9 Months Ended

Sep. 30, 2020

Revenue.

Schedule of revenue by discipline

	Three months ended				Nine months ended
	September 30,				September 30,
	2020		2019		2020		2019
	(in thousands)
Systems	$	70,239	$	36,809	$	229,391	$	131,124
Aftermarket		40,166		32,644		122,970		104,111
	$	110,405	$	69,453	$	352,361	$	235,235

Schedule of revenue by geographic markets

	Three months ended				Nine months ended
	September 30,				September 30,
	2020		2019		2020		2019
	(in thousands)
North America	$	9,022	$	7,681	$	28,598	$	28,670
Asia Pacific		89,995		47,756		293,427		160,398
Europe		11,388		14,016		30,336		46,167
	$	110,405	$	69,453	$	352,361	$	235,235

Schedule of Contract liabilities

	September 30,		December 31,
	2020		2019
	(in thousands)
Contract liabilities	$	16,969	$	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				Nine months ended
	September 30,				September 30,
	2020		2019		2020		2019
	(in thousands)
Balance, beginning of the period	$	30,416	$	14,080	$	29,251	$	22,584
Deferral of revenue		4,030		17,254		10,320		20,887
Recognition of deferred revenue		(17,477)		(3,893)		(22,602)		(16,030)
Balance, ending of the period	$	16,969	$	27,441	$	16,969	$	27,441