SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment	$ 497,909	$ 450,045
Less accumulated depreciation	(267,583)	(217,092)
Net property and equipment	230,326	232,953
Furniture, fixtures, and equipment
Property, Plant and Equipment [Line Items]
Property and equipment	$ 277,014	236,180
Furniture, fixtures, and equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful Lives (in years)	3 years
Furniture, fixtures, and equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful Lives (in years)	12 years
Buildings
Property, Plant and Equipment [Line Items]
Property and equipment	$ 130,712	130,050
Buildings | Minimum
Property, Plant and Equipment [Line Items]
Useful Lives (in years)	3 years
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Useful Lives (in years)	30 years
Corporate aircraft
Property, Plant and Equipment [Line Items]
Useful Lives (in years)	10 years
Property and equipment	$ 11,334	11,334
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	$ 50,616	40,312
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Useful Lives (in years)	3 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Useful Lives (in years)	15 years
Land
Property, Plant and Equipment [Line Items]
Property and equipment	$ 23,658	23,635
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment	$ 4,575	$ 8,534