SEGMENT REPORTING Geographic information (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Revenue from External Customer [Line Items]
Gross premiums written		$ (181,588)	$ (128,205)	$ (553,691)	$ (387,234)
Gross premiums by geographical area as a percentage of total gross premiums		100.00%	100.00%	100.00%	100.00%
U.S. and Caribbean
Revenue from External Customer [Line Items]
Gross premiums written		$ (160,173)	$ (111,926)	$ (483,945)	$ (304,187)
Gross premiums by geographical area as a percentage of total gross premiums		88.20%	87.30%	87.40%	78.60%
Worldwide (1)
Revenue from External Customer [Line Items]
Gross premiums written	[1]	$ (21,237)	$ (13,887)	$ (69,315)	$ (77,554)
Gross premiums by geographical area as a percentage of total gross premiums	[1]	11.70%	10.80%	12.50%	20.00%
Europe
Revenue from External Customer [Line Items]
Gross premiums written		$ (155)	$ (2,334)	$ (392)	$ (5,655)
Gross premiums by geographical area as a percentage of total gross premiums		0.10%	1.80%	0.10%	1.50%
Asia (2)
Revenue from External Customer [Line Items]
Gross premiums written		$ (23)	$ (58)	$ (39)	$ 162	[2]
Gross premiums by geographical area as a percentage of total gross premiums		0.00%	0.10%	0.00%	(0.10%)	[2]

[1] “Worldwide” is comprised of contracts that reinsure risks in more than one geographic area and do not specifically exclude the U.S.

[2] The negative balance represents reversal of premiums due to premium adjustments, termination of contracts or premium returned upon novation or commutation of contracts.