Revenue (Tables)

3 Months Ended

Mar. 31, 2020

Revenue.

Schedule of revenue by discipline

	Three months ended
	March 31,
	2020		2019
	(in thousands)
Systems	$	82,338	$	57,092
Aftermarket		36,653		34,385
	$	118,991	$	91,477

Schedule of revenue by geographic markets

	Three months ended
	March 31,
	2020		2019
	(in thousands)
North America	$	10,661	$	11,607
Asia Pacific		96,828		62,927
Europe		11,502		16,943
	$	118,991	$	91,477

Schedule of Contract liabilities

	March 31,		December 31,
	2020		2019
	(in thousands)
Contract liabilities	$	34,106	$	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
	March 31,
	2020		2019
	(in thousands)
Balance, beginning of the period	$	29,251	$	22,584
Deferral of revenue		9,799		4,078
Recognition of deferred revenue		(4,944)		(6,181)
Balance, ending of the period	$	34,106	$	20,481