Revenue is recognized when control of the promised goods or services are transferred to the Company’s customers in an amount that reflects the consideration the Company expects to be entitled to receive in exchange for those goods or services. The Company accounts for a contract when it has approval and commitment from both parties, the rights of the parties and payment terms are identified, the contract has commercial substance and collectability of consideration is probable.

Contracts with customers may include multiple performance obligations. For such arrangements, the Company allocates revenue to each performance obligation based on its relative standalone selling price. The Company generally determines standalone selling prices based on the prices charged to customers or the expected cost-plus margin.

The following table presents the Company’s revenue disaggregated by revenue source:

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Systems	$	44,315	$	60,113	$	87,087	$	116,216
Software licensing, support and maintenance		7,297		7,547		14,334		15,002
Parts		7,073		6,758		15,150		13,742
Services		2,826		3,058		5,832		5,612
Total revenue	$	61,511	$	77,476	$	122,403	$	150,572

The following table represents a disaggregation of revenue by timing of revenue:

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Point-in-time	$	57,308	$	73,283	$	113,899	$	142,679
Over-time		4,203		4,193		8,504		7,893
Total revenue	$	61,511	$	77,476	$	122,403	$	150,572

See Note 17 of the Notes to the Condensed Consolidated Financial Statements for additional discussion of the Company’s disaggregated revenue in detail.

Revenue from systems is recognized when the Company transfers control of the product to the customer. To indicate transfer of control, the Company must have a present right to payment, legal title must have passed to the customer and the customer must have the significant risks and rewards of ownership. The Company generally transfers control for system sales when the customer or the customer’s agent picks up the system at the Company’s facility. Payment for the majority of the Company’s systems have 80-90% of the invoice amount due within 30 days and the remaining amount due upon completion of installation, recalibration and qualification by the customer. The Company provides an assurance warranty on its systems for a period of twelve to fifteen months against defects in material and workmanship. The Company provides for the estimated cost of product warranties at the time revenue is recognized.

Depending on the terms of the systems arrangement, the Company may also defer the recognition of a portion of the consideration expected to be received because the Company has to satisfy a future obligation (e.g., installation, training and extended warranties). The Company uses an observable price to determine the standalone selling price for separate performance obligations or a cost-plus margin approach when one is not available.

Revenue from software licenses provides the customer with a right to use the software as it exists when made available to the customer. Revenue from software licenses are recognized upfront at the point in time when the software is made available to the customer. Revenue from licensing support and maintenance is recognized as the support and maintenance are provided, which is over the contract period. Payment for software licensing, support and maintenance is generally due in 30 days.

Revenue from parts is recognized when the Company transfers control of the product, which typically occurs when the Company ships the product from its facilities to the customer. Payment for parts is generally due in 30 days.

Revenue from services primarily consists of service contracts, which provide additional maintenance coverage beyond the Company’s assurance warranty on its products, service labor, consulting and training. Revenue from service contracts is recognized ratably over the term of the service contract. Revenue from service labor, consulting and training is recognized as services are performed. Payment for services is generally due in 30 days.

The Company records contract liabilities when the customer has been billed in advance of the Company completing its performance obligations. These amounts are recorded as deferred revenue in the Consolidated Balance Sheets.

	Three Months Ended						Six Months Ended
	June 30,						June 30,
	2019			2018			2019			2018
Balance, beginning of the period	$	8,687		$	8,773		$	8,080		$	7,206
Deferral of revenue		6,130			1,601			11,631			6,154
Recognition of deferred revenue		(5,468	)		(1,575	)		(10,362	)		(4,561	)
Balance, ending of the period	$	9,349		$	8,799		$	9,349		$	8,799