REVENUE RECOGNITION (Tables)

12 Months Ended

Dec. 31, 2018

Revenue from Contract with Customer [Abstract]

The Company's total revenue for the years ended December 31, 2018, 2017 and 2016 was disaggregated geographically as follows:



Year ended December 31, 2018	Product revenue		Service revenue (maintenance)		Service revenue (professional services)		Total revenue
United States	$	169,510	$	132,282	$	35,832	$	337,624
Europe, Middle East and Africa	37,833		46,856		11,794		96,483
Japan	23,108		11,234		5,069		39,411
Other Asia Pacific	30,575		12,321		4,358		47,254
Other	17,988		31,273		7,872		57,133
	$	279,014	$	233,966	$	64,925	$	577,905



Year ended December 31, 2017	Product revenue		Service revenue (maintenance)		Service revenue (professional services)		Total revenue
United States	$	121,121	$	75,040	$	22,896	$	219,057
Europe, Middle East and Africa	23,352		17,471		3,742		44,565
Japan	10,252		10,282		3,855		24,389
Other Asia Pacific	14,693		5,901		1,952		22,546
Other	11,701		6,041		1,643		19,385
	$	181,119	$	114,735	$	34,088	$	329,942



Year ended December 31, 2016	Product revenue		Service revenue (maintenance)		Service revenue (professional services)		Total revenue
United States	$	100,589	$	60,760	$	12,630	$	173,979
Europe, Middle East and Africa	21,073		10,769		2,021		33,863
Japan	12,258		9,831		3,524		25,613
Other Asia Pacific	8,226		3,478		827		12,531
Other	4,235		2,157		213		6,605
	$	146,381	$	86,995	$	19,215	$	252,591

The Company's product revenue from its direct sales program and from indirect sales through its channel partner program for the years ended December 31, 2018, 2017 and 2016 was as follows (in thousands):



	Year ended December 31,
	2018		2017		2016
Indirect sales through channel program	$	69,232	$	43,138	$	38,204
Direct sales	209,782		137,981		108,177
	$	279,014	$	181,119	$	146,381

The Company's product revenue from sales to enterprise customers and from sales to service provider customers for the years ended December 31, 2018, 2017 and 2016 was as follows (in thousands):



	Year ended December 31,
	2018		2017		2016
Sales to enterprise customers	$	57,534	$	35,592	$	28,508
Sales to service provider customers	221,480		145,527		117,873
	$	279,014	$	181,119	$	146,381

Schedule of Customer Assets and Liabilities

The changes in the Company's accounts receivable, unbilled receivables and deferred revenue balances for the year ended December 31, 2018 were as follows (in thousands):



	Accounts receivable		Unbilled accounts receivable			Deferred revenue (current)		Deferred revenue (long-term)
Balance at January 1, 2018	$	149,122	$	16,034		$	100,571	$	14,184
Increase (decrease), net	25,188		(2,491		)	4,516		3,388
Balance at December 31, 2018	$	174,310	$	13,543		$	105,087	$	17,572

Schedule of Timing of Performance Obligation

The Company's typical performance obligations include the following:



Performance Obligation	When Performance Obligation is Typically Satisfied	When Payment is Typically Due
Software and Product Revenue
Software licenses (perpetual or term)	Upon transfer of control; typically, when made available for download (point in time)	Generally, within 30 days of invoicing except for term licenses, which may be paid for over time

Software licenses (subscription)	Upon activation of hosted site (over time)	Generally, within 30 days of invoicing

Appliances	When control of the appliance passes to the customer; typically, upon delivery (point in time)	Generally, within 30 days of invoicing

Software upgrades	Upon transfer of control; typically, when made available for download (point in time)	Generally, within 30 days of invoicing

Customer Support Revenue
Customer support	Ratably over the course of the support contract (over time)	Generally, within 30 days of invoicing

Professional Services
Other professional services (excluding training services)	As work is performed (over time)	Generally, within 30 days of invoicing (upon completion of services)

Training	When the class is taught (point in time)	Generally, within 30 days of services being performed