OTHER COMPREHENSIVE INCOME (LOSS) - Component of other comprehensive income (loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Before tax amount
Other comprehensive income (loss), before tax amount	$ (202,694)	$ 219,197	$ 69,950
Tax (expense) benefit
Other comprehensive income (loss), tax (expense) benefit	700	(4,974)	(3,326)
Net of tax amount
Other comprehensive income (loss), net of tax amount	(201,994)	214,223	66,624
Unrealized gains (losses) on available for sale investments, net of tax
Before tax amount
Unrealized investment gains (losses) arising during the year	(297,259)	211,151	10,165
Adjustment for reclassification of net realized investment (gains) losses and OTTI losses recognized in net income	105,730	(33,892)	60,423
Other comprehensive income (loss), before tax amount	(191,529)	177,259	70,588
Tax (expense) benefit
Unrealized investment gains (losses) arising during the year	5,528	(5,732)	(5,093)
Adjustment for reclassification of net realized investment (gains) losses and OTTI losses recognized in net income	(4,828)	758	1,767
Other comprehensive income (loss), tax (expense) benefit	700	(4,974)	(3,326)
Net of tax amount
Unrealized investment gains (losses) arising during the year	(291,731)	205,419	5,072
Adjustment for reclassification of net realized investment (gains) losses and OTTI losses recognized in net income	100,902	(33,134)	62,190
Other comprehensive income (loss), net of tax amount	(190,829)	172,285	67,262
Non-credit portion of OTTI losses
Before tax amount
Other comprehensive income (loss), before tax amount	0	0	0
Tax (expense) benefit
Other comprehensive income (loss), tax (expense) benefit	0	0	0
Net of tax amount
Other comprehensive income (loss), net of tax amount	0	0	0
Foreign currency translation adjustment
Before tax amount
Other comprehensive income (loss), before tax amount	(11,165)	41,938	(638)
Tax (expense) benefit
Other comprehensive income (loss), tax (expense) benefit	0	0	0
Net of tax amount
Other comprehensive income (loss), net of tax amount	$ (11,165)	$ 41,938	$ (638)