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, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
CONDENSED STATEMENTS OF EARNINGS AND COMPREHENSIVE EARNINGS
Net investment income	$ 14,446	$ 14,187	$ 13,238	$ 13,005	$ 13,153	$ 13,504	$ 13,048	$ 13,370	$ 54,876	$ 53,075	$ 54,644
Net realized gains (losses)	5,111	35	(1,359)	624	11,283	9,252	2,710	11,400	4,411	34,645	39,829
Equity in earnings of unconsolidated investees									17,224	10,833	10,914
Interest expense on debt									(7,426)	(7,426)	(7,426)
Loss before income taxes	24,972	(862)	34,036	26,443	38,006	31,142	42,341	45,593	84,589	157,082	196,682
Income tax benefit									(20,439)	42,162	59,138
Net earnings	$ 57,258	$ 1,734	$ 26,208	$ 19,828	$ 32,187	$ 22,263	$ 29,077	$ 31,393	105,028	114,920	137,544
Unrealized gains (losses) on securities:
Other comprehensive earnings (loss), net of tax									35,309	(1,164)	(47,609)
Comprehensive earnings									140,337	113,756	89,935
PARENT COMPANY
CONDENSED STATEMENTS OF EARNINGS AND COMPREHENSIVE EARNINGS
Net investment income									647	942	810
Net realized gains (losses)									(36)	(360)	139
Equity in earnings of unconsolidated investees									14,436	9,764	9,893
Selling, general and administrative expenses									(11,340)	(10,170)	(9,837)
Interest expense on debt									(7,426)	(7,426)	(7,426)
Loss before income taxes									(3,719)	(7,250)	(6,421)
Income tax benefit									(16,601)	(8,467)	(5,499)
Net earnings (loss) before equity in net earnings of subsidiaries									12,882	1,217	(922)
Equity in net earnings of subsidiaries									92,146	113,703	138,466
Net earnings									105,028	114,920	137,544
Unrealized gains (losses) on securities:
Unrealized holding gains (losses) arising during the period									21	308	(40)
Less: reclassification adjustment for losses (gains) included in net earnings									6	(131)	(90)
Other Comprehensive Income (Loss), Net of Tax, Total									27	177	(130)
Equity in other comprehensive earnings (loss) of subsidiaries/investees									35,282	(1,341)	(47,479)
Other comprehensive earnings (loss), net of tax									35,309	(1,164)	(47,609)
Comprehensive earnings									$ 140,337	$ 113,756	$ 89,935