INCOME TAXES (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Tax discounting of claim reserves	$ 18,327,000	$ 20,020,000
Unearned premium offset	17,864,000	16,528,000
Deferred compensation	2,700,000	1,435,000
Stock option expense	2,702,000	2,283,000
Other	616,000	578,000
Deferred tax assets before allowance	42,209,000	40,844,000
Total deferred tax assets	42,209,000	40,844,000
Deferred tax liabilities:
Net unrealized appreciation of securities	22,177,000	51,448,000
Deferred policy acquisition costs	17,836,000	16,320,000
Deferred Tax Liabilities Discounting Of Unpaid Losses TCJA Offset	5,203,000	9,466,000
Book/tax depreciation	3,133,000	3,159,000
Intangible assets	1,711,000	584,000
Undistributed earnings of unconsolidated investees	15,811,000	13,431,000
Other	576,000	204,000
Total deferred tax liabilities	66,447,000	94,612,000
Net deferred tax liability	$ (24,238,000)	$ (53,768,000)
U.S. federal tax rate (as a percent)	21.00%	35.00%	35.00%
Increase (reduction) in taxes resulting from:
Provision for income taxes at the statutory rate of 21% in 2018 and 35% in 2017	$ 14,192,000	$ 29,606,000	$ 54,979,000
Enactment Of Tax Cuts And Jobs Act	(2,268,000)	(32,821,000)
Excess tax benefit on share-based compensation	(4,533,000)	(5,798,000)
Dividends received deduction	(775,000)	(2,025,000)	(2,216,000)
ESOP dividends paid deduction	(1,184,000)	(2,905,000)	(3,302,000)
Tax-exempt interest income	(1,795,000)	(4,671,000)	(4,263,000)
Unconsolidated investee dividends		(1,351,000)	(2,772,000)
Other items, net	(235,000)	(474,000)	(264,000)
Income tax expense (benefit)	$ 3,402,000	$ (20,439,000)	$ 42,162,000
Reconciliation of income tax expense rate to the U.S. federal tax rate
U.S. federal tax rate (as a percent)	21.00%	35.00%	35.00%
Enactment of Tax Cuts and Jobs Act (TCJA)	(3.40%)	(38.80%)
Excess tax benefit on share-based compensation	(6.70%)	(6.90%)
Effective rate reduction due to dividend received (as a percent)	(1.10%)	(2.40%)	(1.40%)
Effective rate reduction due to dividend paid to ESOP (as a percent)	(1.80%)	(3.40%)	(2.10%)
Effective rate reduction due to tax exempt interest income (as a percent)	(2.70%)	(5.50%)	(2.70%)
Effective rate reduction due to unconsolidated investee dividends		(1.60%)	(1.80%)
Effective rate reduction due to other items, net (as a percent)	(0.30%)	(0.60%)	(0.20%)
Effective Income Tax Rate Reconciliation, Percent, Total	5.00%	(24.20%)	26.80%
Income tax expense (benefit)	$ 3,402,000	$ (20,439,000)	$ 42,162,000
Effective tax rates (as a percent)	5.00%	(24.20%)	26.80%
Capital gains rate (as a percent)	21.00%
Dividend received	$ 9,900,000	$ 0	$ 9,900,000
Lower tax rate (as a percent)	7.40%		7.00%
Effective rate reduction due to dividends paid to ESOP (as a percent)	1.80%	3.40%	2.10%
Expected effective tax rate when deferred items reverse in future years (as a percent)	21.00%
Federal and state income taxes paid	$ 16,400,000	$ 10,400,000	$ 26,900,000