Summary of Investments (Unrealized Appreciation) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Change in net unrealized investment appreciation
Available-for-sale fixed maturities	$ (59,126)	$ 7,043
Available-for-sale equity securities	0	5,795
Deferred policy acquisition costs	7,274	(1,277)
Income tax effect	10,890	(4,046)
Net unrealized investment depreciation of discontinued operations, sold	6,714	0
Cumulative change in accounting principles			$ (191,244)	$ 0
Total change in net unrealized investment appreciation, net of tax	$ (225,492)	$ 7,515