INCOME TAXES - Operating and capital loss carryforwards and tax credits (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Singapore
Operating Loss And Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	$ 79,445	$ 77,467
United Kingdom
Operating Loss And Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	413,504	126,839
Tax credit	398	14,310
Ireland
Operating Loss And Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	12,756	0
Tax credit	2,248	3,566
Ireland | Capital loss carryforward
Operating Loss And Tax Credit Carryforwards [Line Items]
Capital loss carryforwards	716	716
U.S.
Operating Loss And Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	15,062	115,236
U.S. alternative minimum tax credit	6,026	12,052
Lloyd's | United Kingdom
Operating Loss And Tax Credit Carryforwards [Line Items]
Operating loss carryforwards	$ 403,000	$ 113,000