REVENUE RECOGNITION - Summary of New Accounting Adoption Impact on Consolidated Statements of Income (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenues	$ 78,002	$ 77,038	$ 223,870	$ 206,492
Cost of revenues	52,738	60,577	157,589	169,438
Gross profit	25,264	16,461	66,281	37,054
Operating expenses:
Research and development	8,165	7,397	25,247	24,949
Sales and marketing	7,375	5,453	20,430	18,186
General and administrative	7,510	5,441	21,423	16,238
Restructuring charges	2,588	4,071	2,588	14,927
Total operating expenses	25,638	22,362	69,688	74,300
Loss from operations	(374)	(5,901)	(3,407)	(37,246)
Other expense, net
Interest expense	(2,469)	(1,760)	(7,031)	(5,979)
Other expense	(379)	623	(1,077)	1,771
Total other expense, net	(2,848)	(1,137)	(8,108)	(4,208)
Loss before income taxes	(3,222)	(7,038)	(11,515)	(41,454)
Income tax provision	(248)	184	(821)	(798)
Net loss	$ (3,470)	$ (6,854)	$ (12,336)	$ (42,252)
Net loss per share:
Basic and diluted (in usd per share)	$ (0.03)	$ (0.08)	$ (0.13)	$ (0.52)
Shares used in per share calculation:
Basic and diluted (in shares)	102,798	84,862	97,257	81,993
Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenues	$ 323		$ 2,781
Cost of revenues	413		1,409
Gross profit	(90)		1,372
Operating expenses:
Research and development	0		0
Sales and marketing	0		58
General and administrative	0		0
Restructuring charges	0		0
Total operating expenses	0		58
Loss from operations	(90)		1,314
Other expense, net
Interest expense	0		0
Other expense	0		0
Total other expense, net	0		0
Loss before income taxes	(90)		1,314
Income tax provision	0		0
Net loss	$ (90)		$ 1,314
Net loss per share:
Basic and diluted (in usd per share)	$ 0.00		$ 0.01
Without Adoption of Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenues	$ 77,679		$ 221,089
Cost of revenues	52,325		156,180
Gross profit	25,354		64,909
Operating expenses:
Research and development	8,165		25,247
Sales and marketing	7,375		20,372
General and administrative	7,510		21,423
Restructuring charges	2,588		2,588
Total operating expenses	25,638		69,630
Loss from operations	(284)		(4,721)
Other expense, net
Interest expense	(2,469)		(7,031)
Other expense	(379)		(1,077)
Total other expense, net	(2,848)		(8,108)
Loss before income taxes	(3,132)		(12,829)
Income tax provision	(248)		(821)
Net loss	$ (3,380)		$ (13,650)
Net loss per share:
Basic and diluted (in usd per share)	$ (0.03)		$ (0.14)
Shares used in per share calculation:
Basic and diluted (in shares)	102,798		97,257