GOODWILL AND INTANGIBLE ASSETS - Analysis of goodwill and intangible assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill
Goodwill, gross		$ 97,092,000	$ 42,237,000	$ 42,237,000
Accumulated translation adjustment		4,911,000	4,911,000	4,911,000
Goodwill, net of accumulated translation adjustment	$ 102,003,000	102,003,000	47,148,000	47,148,000
Acquired during the year		54,855,000
Intangible assets with an indefinite life
Gross amount		120,784,000	26,036,000	26,036,000
Accumulated translation adjustment		0	0	0
Intangible assets with an indefinite life, net	120,784,000	120,784,000	26,036,000
Acquired during the year		94,748,000
Intangible assets with a finite life
Gross amount		410,575,000	23,030,000	23,030,000
Accumulated amortization		(66,534,000)	(11,165,000)	(9,356,000)
Accumulated translation adjustment		0	0	0
Intangible assets with a finite life, net	156,498,000	344,041,000	11,865,000	13,674,000
Acquired during the year		387,545,000
Amortization	(184,043,000)	(55,369,000)	(1,809,000)
Impairment charge	(3,500,000)
Total
Gross amount		628,451,000	91,303,000	91,303,000
Accumulated amortization		(66,534,000)	(11,165,000)	(9,356,000)
Accumulated translation adjustment		4,911,000	4,911,000	4,911,000
Goodwill and intangible assets net balance	379,285,000	566,828,000	85,049,000	$ 86,858,000
Acquired during the year		537,148,000
Amortization	(184,043,000)	(55,369,000)	(1,809,000)
Impairment charge	$ (3,500,000)	$ 0	$ 0