REVENUE - Effect on Balance Sheet (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Accounts receivables and contract assets, net of allowance of $661	$ 73,522	$ 72,292	$ 70,824
Prepaid expense and other current assets	4,038	3,396	4,467
Deferred tax asset	2,502	1,972	2,521
Liabilities
Contract liabilities	4,800	6,480	8,898
Accrued expenses	17,738	21,619	21,486
Deferred tax liability	1,866	1,664	1,569
Stockholders' equity
Accumulated deficit	(153,248)	(155,776)	(157,814)
Accounts receivables and contract assets, allowances	661	503	$ 503
Remaining performance obligations	$ 97,900
Practical expedient incremental costs to obtain a contract	true
As Previously Reported Under ASC 605 | ASU 2014-09 (“ASC Topic 606”)
Assets
Accounts receivables and contract assets, net of allowance of $661	$ 71,791	70,824
Prepaid expense and other current assets	6,112	4,467
Deferred tax asset	3,051	2,521
Liabilities
Contract liabilities	10,920	8,898
Accrued expenses	17,588	21,486
Deferred tax liability	1,064	1,569
Stockholders' equity
Accumulated deficit	(157,524)	(157,814)
Adjustments | ASU 2014-09 (“ASC Topic 606”)
Assets
Accounts receivables and contract assets, net of allowance of $661	(1,731)	1,468
Prepaid expense and other current assets	2,074	(1,071)
Deferred tax asset	549	(549)
Liabilities
Contract liabilities	6,120	(2,418)
Accrued expenses	(150)	133
Deferred tax liability	(802)	95
Stockholders' equity
Accumulated deficit	$ (4,276)	$ 2,038