SCHEDULE II-CONDENSED FINANCIAL INFORMATION OF REGISTRANT (PARENT COMPANY) - Statements of Earnings and Comprehensive Earnings (Details) - USD ($) $ in Thousands	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
CONDENSED STATEMENTS OF EARNINGS AND COMPREHENSIVE EARNINGS
Net investment income	$ 16,962	$ 16,314	$ 14,577	$ 14,232	$ 14,446	$ 14,187	$ 13,238	$ 13,005	$ 62,085	$ 54,876	$ 53,075
Net realized gains									63,624	6,970	34,740
Equity in earnings of unconsolidated investees									16,056	17,224	10,833
Interest expense on debt									(7,437)	(7,426)	(7,426)
Earnings before income taxes	(32,708)	46,349	39,562	14,378	24,972	(862)	34,036	26,443	67,581	84,589	157,082
Income tax benefit									3,402	(20,439)	42,162
Net earnings	$ (20,660)	$ 39,372	$ 33,251	$ 12,216	$ 57,258	$ 1,734	$ 26,208	$ 19,828	64,179	105,028	114,920
Unrealized gains (losses) on securities:
Other comprehensive earnings (loss), net of tax									(33,997)	35,309	(1,164)
Comprehensive earnings									30,182	140,337	113,756
PARENT COMPANY
CONDENSED STATEMENTS OF EARNINGS AND COMPREHENSIVE EARNINGS
Net investment income									648	647	942
Net realized gains									(142)	(36)	(360)
Equity in earnings of unconsolidated investees									12,471	14,436	9,764
Selling, general and administrative expenses									(9,427)	(11,340)	(10,170)
Interest expense on debt									(7,437)	(7,426)	(7,426)
Earnings before income taxes									(3,887)	(3,719)	(7,250)
Income tax benefit									(2,359)	(16,601)	(8,467)
Net earnings (loss) before equity in net earnings of subsidiaries									(1,528)	12,882	1,217
Equity in net earnings of subsidiaries									65,707	92,146	113,703
Net earnings									64,179	105,028	114,920
Unrealized gains (losses) on securities:
Unrealized holding gains (losses) arising during the period									710	21	308
Less: reclassification adjustment for losses (gains) included in net earnings									112	6	(131)
Other Comprehensive Income (Loss), Net of Tax, Total									822	27	177
Equity in other comprehensive earnings (loss) of subsidiaries/investees									(34,819)	35,282	(1,341)
Other comprehensive earnings (loss), net of tax									(33,997)	35,309	(1,164)
Comprehensive earnings									$ 30,182	$ 140,337	$ 113,756