LEASES - IMPACT OF NEW LEASES GUIDANCE (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Lease, Cost [Abstract]
Variable rent expense	$ 1,329	$ 1,032
Amortization of deferred rent	38	104
Facility
Lease, Cost [Abstract]
Operating lease costs	8,856	7,662
Office
Lease, Cost [Abstract]
Operating lease costs	850	635
Cost of services
Lease, Cost [Abstract]
Operating lease costs	9,706	8,297
General and administrative expense
Lease, Cost [Abstract]
Operating lease costs	$ 30	$ 33

Amount of single lease cost, calculated by allocation of remaining cost of lease over remaining lease term. Includes, but is not limited to, single lease cost, after impairment of right-of-use asset, calculated by amortization of remaining right-of-use asset and accretion of lease liability.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 55
-Paragraph 53
-URI http://asc.fasb.org/extlink&oid=77888399&loc=SL77918982-209971

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918686-209980

Name:	us-gaap_OperatingLeaseCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration