ORGANIZATION AND BASIS OF PRESENTATION (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017	Jun. 30, 2017	Jan. 01, 2017	Dec. 31, 2016
Summary of significant accounting policies
Increase in deferred revenue	$ 12,955		$ 9,802
Increase in other current liabilities	7,912		9,414
Decrease in retained earnings	(603,343)		(626,600)
Cumulative effect of accounting changes		$ 10,448			$ 0
Restricted cash	5,728		3,837	$ 4,200		$ 4,127
Operating lease, right-of-use, estimated asset and liability (approximate)	16,800
Accounting Standards Update 2014-09 | Adjustments
Summary of significant accounting policies
Increase in deferred revenue	(4,048)	11,200
Increase unbilled accounts receivable		1,100
Increase in other current liabilities	(2,303)	300
Decrease in retained earnings	(6,454)	10,400
Accounting Standards Update 2016-01 | Accumulated other comprehensive income (loss)
Summary of significant accounting policies
Cumulative effect of accounting changes		$ 733
Lenders One
Summary of significant accounting policies
Total assets	2,700		4,600
Total liabilities	$ 900		$ 3,100