SCHEDULE II-CONDENSED FINANCIAL INFORMATION OF REGISTRANT (PARENT COMPANY) - Statements of Cash Flows (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Adjustments to reconcile net losses to net cash provided by (used in) operating activities:
Net realized gains (losses)	$ (15,507,000)	$ (18,647,000)	$ (20,849,000)	$ (8,404,000)	$ (5,111,000)	$ (35,000)	$ 1,359,000	$ (624,000)	$ (63,407,000)	$ (4,411,000)	$ (34,645,000)
Depreciation									7,042,000	6,944,000	6,430,000
Other items, net									6,171,000	16,368,000	17,699,000
Change in:
Stock option excess tax benefit											(9,576,000)
Changes in investment in unconsolidated investees:
Undistributed earnings									(16,056,000)	(17,224,000)	(10,833,000)
Dividends received									9,900,000	0	9,900,000
Net Cash Provided by Operating Activities									217,102,000	197,525,000	174,463,000
Purchase of:
Fixed income, available-for-sale									(725,675,000)	(430,727,000)	(557,067,000)
Short-term investments, net									(1,570,000)	(4,965,000)
Property and equipment									(6,087,000)	(9,238,000)	(16,155,000)
Sale of:
Fixed income, available-for-sale									395,019,000	168,760,000	329,091,000
Short-term investments, net											2,564,000
Property and equipment									167,000	128,000	1,688,000
Call or maturity of:
Fixed income, available-for-sale									187,380,000	195,617,000	141,255,000
Net Cash Used in Investing Activities, Total									(134,209,000)	(81,212,000)	(53,622,000)
Cash flows from financing activities
Excess tax benefit from exercise of stock options											9,576,000
Stock plan share issuance									(6,076,000)	(3,502,000)	741,000
Net Cash Used in Financing Activities, Total									(77,024,000)	(110,311,000)	(113,653,000)
Net increase (decrease) in cash									5,869,000	6,002,000	7,188,000
Cash at the beginning of the period				24,271,000				18,269,000	24,271,000	18,269,000	11,081,000
Cash at the end of the period	30,140,000				24,271,000				30,140,000	24,271,000	18,269,000
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									(1,528,000)	12,882,000	1,217,000
Adjustments to reconcile net losses to net cash provided by (used in) operating activities:
Net realized gains (losses)									142,000	36,000	360,000
Depreciation									68,000	77,000	196,000
Other items, net									(471,000)	595,000	560,000
Change in:
Affiliate balances receivable/payable									1,187,000	(930,000)	(535,000)
Federal income taxes									3,430,000	(6,874,000)	9,762,000
Stock option excess tax benefit											(9,576,000)
Changes in investment in unconsolidated investees:
Undistributed earnings									(12,471,000)	(14,436,000)	(9,764,000)
Dividends received									9,900,000		9,900,000
Net Cash Provided by Operating Activities									257,000	(8,650,000)	2,120,000
Purchase of:
Fixed income, available-for-sale									(73,812,000)	(5,773,000)	(12,844,000)
Short-term investments, net										(47,000)
Sale of:
Fixed income, available-for-sale									12,056,000	24,771,000	4,981,000
Short-term investments, net									70,000		63,000
Property and equipment										128,000
Call or maturity of:
Fixed income, available-for-sale									75,662,000	3,499,000	6,859,000
Cash dividends received-subsidiaries									73,363,000	107,000,000	123,600,000
Net Cash Used in Investing Activities, Total									87,339,000	129,578,000	122,659,000
Cash flows from financing activities
Excess tax benefit from exercise of stock options											9,576,000
Stock plan share issuance									(6,076,000)	(3,502,000)	741,000
Cash dividends paid									(90,662,000)	(124,247,000)	(133,771,000)
Net Cash Used in Financing Activities, Total									(84,586,000)	(120,745,000)	(124,936,000)
Net increase (decrease) in cash									3,010,000	183,000	(157,000)
Cash at the beginning of the period				$ 204,000				$ 21,000	204,000	21,000	178,000
Cash at the end of the period	$ 3,214,000				$ 204,000				3,214,000	204,000	21,000
Interest paid on outstanding debt									$ 7,300,000	$ 7,300,000	$ 7,300,000