REINSURANCE - Summary of Premiums and Losses (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
REINSURANCE
Maximum amount beyond which net loss on any individual risk is limited through the purchase of reinsurance	$ 3,000								$ 3,000
WRITTEN
Direct									1,039,955	$ 934,913	$ 848,153
Reinsurance assumed									25,047	48,303	37,159
Reinsurance ceded									(204,665)	(160,041)	(135,458)
Net									860,337	823,175	749,854
EARNED
Direct									981,121	896,234	835,118
Reinsurance assumed									40,173	41,926	32,521
Reinsurance ceded									(182,183)	(146,794)	(129,702)
Net amount	$ 215,626	$ 211,255	$ 207,541	$ 204,689	$ 204,002	$ 200,815	$ 196,522	$ 190,027	839,111	791,366	737,937
LOSSES AND SETTLEMENT EXPENSES INCURRED
Direct									521,055	560,421	486,986
Reinsurance assumed									21,951	20,376	16,072
Reinsurance ceded									(129,590)	(152,604)	(101,474)
Net									$ 413,416	$ 428,193	$ 401,584