Summary of Significant Accounting Policies (AOCI) (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
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other net investment gains (losses)									$ 8,423	$ 14,875	$ 13,070
Earnings before Federal income taxes									141,507	144,555	152,862
Federal income taxes									24,749	34,134	51,970
Net earnings	$ 21,776	$ 35,641	$ 32,466	$ 26,875	$ 39,587	$ 21,813	$ 25,483	$ 23,538	116,758	110,421	100,892
Accumulated other comprehensive income (loss) | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other net investment gains (losses)									3,441	5,348	3,316
Net OTTI losses recognized in earnings									0	(112)	0
Earnings before Federal income taxes									3,441	5,236	3,316
Federal income taxes									723	1,833	1,161
Net earnings									$ 2,718	$ 3,403	$ 2,155