Consolidation and Basis of Presentation (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other net investment gains (losses)	$ 2,074	$ 5,426	$ 10,906	$ 10,589
Earnings before Federal income taxes	33,858	48,651	108,122	114,833
Federal income taxes	12,045	14,915	37,288	37,553
Net earnings	21,813	33,736	70,834	77,280
Unrealized Gains and Losses on Available-for-sale Securities \| Amount Reclassified From Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other net investment gains (losses)	1,519	2,151	4,224	3,033
Net OTTI losses recognized in earnings	0	0	0	0
Earnings before Federal income taxes	1,519	2,151	4,224	3,033
Federal income taxes	532	753	1,478	1,062
Net earnings	$ 987	$ 1,398	$ 2,746	$ 1,971

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting.

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