HISTORICAL LOSS AND LAE DEVELOPMENT - Unpaid Losses and Settlement Expenses (Details) - USD ($) $ in Thousands	6 Months Ended
Jun. 30, 2020	Jun. 30, 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	253,031	239,053
Prior accident years	(40,808)	(40,837)
Total incurred	212,223	198,216
Loss and LAE payments for claims incurred:
Current accident year	(25,588)	(23,624)
Prior accident year	(148,885)	(126,972)
Total paid	(174,473)	(150,596)
Net	1,226,240	1,143,969
Unpaid losses and LAE at year end
Gross	1,590,996	1,506,279
Ceded	(364,756)	(362,310)
Net	$ 1,226,240	$ 1,143,969
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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