SCHEDULE II-CONDENSED FINANCIAL INFORMATION OF REGISTRANT (PARENT COMPANY) - Statements of Cash Flows (Details) - USD ($)	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
Cash flows from operating activities
Earnings (loss) before equity in net earnings of subsidiaries									$ 191,642,000	$ 64,179,000	$ 105,028,000
Adjustments to reconcile net losses to net cash provided by (used in) operating activities:
Net realized gains (losses)	$ (477,000)	$ (3,211,000)	$ (4,764,000)	$ (9,068,000)	$ (15,507,000)	$ (18,647,000)	$ (20,849,000)	$ (8,404,000)	(17,520,000)	(63,407,000)	(4,411,000)
Depreciation									8,164,000	7,042,000	6,944,000
Other items, net									25,341,000	6,171,000	16,368,000
Changes in investment in unconsolidated investees:
Undistributed earnings									(20,960,000)	(16,056,000)	(17,224,000)
Dividends received									13,200,000	9,900,000	0
Net Cash Provided by Operating Activities									276,917,000	217,102,000	197,525,000
Purchase of:
Fixed income, available-for-sale									(539,726,000)	(725,675,000)	(430,727,000)
Property and equipment									(6,955,000)	(6,087,000)	(9,238,000)
Sale of:
Fixed income, available-for-sale									196,558,000	395,019,000	168,760,000
Property and equipment										167,000	128,000
Call or maturity of:
Fixed income, available-for-sale									201,383,000	187,380,000	195,617,000
Payments for (Proceeds from) Short-term Investments [Abstract]
Net proceeds from sale (purchase) of short-term investments									11,550,000	(1,570,000)	(4,965,000)
Net cash used in investing activities									(184,753,000)	(134,209,000)	(81,212,000)
Cash flows from financing activities
Proceeds from stock option exercises									9,490,000	6,076,000	3,502,000
Net cash used in financing activities									(76,101,000)	(77,024,000)	(110,311,000)
Net increase (decrease) in cash									16,063,000	5,869,000	6,002,000
Cash at the beginning of the period				30,140,000				24,271,000	30,140,000	24,271,000	18,269,000
Cash at the end of the period	46,203,000				30,140,000				46,203,000	30,140,000	24,271,000
Interest paid on outstanding debt									7,300,000	7,300,000	7,300,000
PARENT COMPANY
Cash flows from operating activities
Earnings (loss) before equity in net earnings of subsidiaries									426,000	(1,528,000)	12,882,000
Adjustments to reconcile net losses to net cash provided by (used in) operating activities:
Net realized gains (losses)									(463,000)	142,000	36,000
Depreciation									68,000	68,000	77,000
Other items, net									2,487,000	(471,000)	595,000
Change in:
Affiliate balances receivable/payable									1,180,000	1,187,000	(930,000)
Federal income taxes									(1,673,000)	3,430,000	(6,874,000)
Changes in investment in unconsolidated investees:
Undistributed earnings									(13,592,000)	(12,471,000)	(14,436,000)
Dividends received									13,200,000	9,900,000
Net Cash Provided by Operating Activities									1,633,000	257,000	(8,650,000)
Purchase of:
Fixed income, available-for-sale									(2,507,000)	(73,812,000)	(5,773,000)
Sale of:
Fixed income, available-for-sale									14,273,000	12,056,000	24,771,000
Property and equipment											128,000
Call or maturity of:
Fixed income, available-for-sale									29,501,000	75,662,000	3,499,000
Payments for (Proceeds from) Short-term Investments [Abstract]
Net proceeds from sale (purchase) of short-term investments										70,000	(47,000)
Cash dividends received-subsidiaries									34,003,000	73,363,000	107,000,000
Net cash used in investing activities									75,270,000	87,339,000	129,578,000
Cash flows from financing activities
Proceeds from stock option exercises									9,490,000	6,076,000	3,502,000
Cash dividends paid									(93,315,000)	(90,662,000)	(124,247,000)
Proceeds from (Payments for) Other Financing Activities									4,058,000
Net cash used in financing activities									(79,767,000)	(84,586,000)	(120,745,000)
Net increase (decrease) in cash									(2,864,000)	3,010,000	183,000
Cash at the beginning of the period				$ 3,214,000				$ 204,000	3,214,000	204,000	21,000
Cash at the end of the period	$ 350,000				$ 3,214,000				350,000	3,214,000	204,000
Interest paid on outstanding debt									$ 7,300,000	$ 7,300,000	$ 7,300,000