HISTORICAL LOSS AND LAE DEVELOPMENT - Unpaid Losses and Settlement Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Unpaid losses and LAE at beginning of year:
Gross	$ 1,574,352	$ 1,461,348
Ceded	(384,517)	(364,999)
Net	1,189,835	1,096,349
Increase (decrease) in incurred losses and LAE:
Current accident year	126,194	113,930
Prior accident years	(15,173)	(19,633)
Total incurred	111,021	94,297
Loss and LAE payments for claims incurred:
Current accident year	(9,295)	(5,531)
Prior accident year	(81,897)	(70,145)
Total paid	(91,192)	(75,676)
Net	1,208,319	1,114,970
Unpaid losses and LAE at year end
Gross	1,574,760	1,479,344
Ceded	(366,441)	(364,374)
Net	$ 1,208,319	$ 1,114,970
Accounting Standards Update 2016-13 \| Restatement Adjustment
Adoption impact of ASU 2016-13
Adoption impact of ASU 2016-13 on reinsurance balances recoverable			$ (1,345)

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