STOCK-BASED AWARDS (Details) - USD ($)		12 Months Ended
	Jan. 23, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 14,356,000	$ 4,077,000	$ 4,891,000
Options
Outstanding—end of year (in shares)		0
tZero.com, Inc.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 4,848,000	0	0
Restricted stock awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 9,096,000	$ 4,056,000	$ 4,891,000
Units
Outstanding-beginning of year (in shares)		540,000	560,000	349,000
Granted at fair value (in shares)		387,000	310,000	541,000
Vested (in shares)		(234,000)	(212,000)	(219,000)
Forfeited (in shares)		(134,000)	(118,000)	(111,000)
Outstanding-end of period (in shares)		559,000	540,000	560,000
Weighted Average Grant Date Fair Value
Outstanding-beginning of year (in dollars per share)		$ 17.05	$ 17.46	$ 24.80
Granted at fair value (in dollars per share)		65.42	17.75	14.52
Vested (in dollars per share)		17.68	19.58	22.57
Forfeited (in dollars per share)		42.85	16.21	16.52
Outstanding-end of period (in dollars per share)		$ 44.08	$ 17.05	$ 17.46
Restricted stock awards | tZero.com, Inc.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 4,000,000
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 0	$ 0	$ 0
Options
Outstanding—beginning of year (in shares)		0	156,000	204,000
Exercised (in shares)		0	(39,000)	(42,000)
Expired/Forfeited (in shares)		0	(117,000)	(6,000)
Outstanding—end of year (in shares)		0	0	156,000
Options exercisable at year-end (in shares)		0	0	156,000
Weighted Average Exercise Price
Outstanding—beginning of year (in dollars per share)		$ 0.00	$ 17.33	$ 17.27
Exercised (in dollars per share)		0.00	16.90	17.08
Expired/Forfeited (in dollars per share)		0.00	17.48	17.08
Outstanding—end of year (in dollars per share)		0.00	0.00	17.33
Options exercisable at year-end (in dollars per share)		$ 0.00	$ 0.00	$ 17.33
Stock options | Medici Ventures Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense		$ 412,000	$ 21,000	$ 0