COMMITMENTS AND CONTINGENCIES - Operating Leases (Details) $ in Thousands, £ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 GBP (£) ft²	Jul. 31, 2015 USD ($)	Aug. 31, 2013 USD ($) ft²
Property Subject to or Available for Operating Lease [Line Items]
Operating leases, rent expense	$ 2,900	$ 3,000	$ 3,000
2019	2,706
2020	2,089
2021	1,654
2022	1,703
2023	1,755
Thereafter	2,418
Total	$ 12,325
Corporate Headquarters, Atlanta, GA
Property Subject to or Available for Operating Lease [Line Items]
Lease, term of contract						130 months
Area of real estate property (sq ft) | ft²						76,880
Tenant improvement allowance						$ 3,800
Total						$ 16,000
Data Center Space, Atlanta, GA
Property Subject to or Available for Operating Lease [Line Items]
Lease, term of contract					60 months
Total					$ 2,300
Office, Victoria, London
Property Subject to or Available for Operating Lease [Line Items]
Lease, term of contract				40 months
Area of real estate property (sq ft) | ft²				5,295
Total | £				£ 0.8