FEDERAL INCOME TAX (Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation Of Consolidated Federal Income Tax Expense (Benefit) [Line Items]
Consolidated federal income tax expense (benefit)	$ (29,220)	$ 8,379	$ 30,050
Consolidated federal income tax expense (benefit), discontinued operations	4,490	384	2,275
Continuing and Discontinuing Operations
Reconciliation Of Consolidated Federal Income Tax Expense (Benefit) [Line Items]
Computed expected income tax expense	9,202	20,533	42,508
Impact of enactment of Tax Act	(21,884)	0	0
Tax-exempt municipal bond interest income	(8,875)	(8,330)	(7,669)
Nontaxable dividend income	(1,540)	(1,317)	(1,337)
Valuation allowance reduction	(547)	(547)	(548)
Other, net	(1,086)	(1,576)	(629)
Consolidated federal income tax expense (benefit)	$ (24,730)	$ 8,763	$ 32,325