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Realized and Unrealized Investment Gains (Losses) (Change in Unrealized Gains (Losses) of Available For Sales Securities) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment gains	$ (160,848)	$ (9,571)
Income tax benefit	35,076	740
Noncontrolling interests	(11)	19
Total change in unrealized gains	(125,783)	(8,812)
Increase (decrease) in accumulated other comprehensive income	(258,982)			$ 68,541
Debt securities
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment gains	(159,727)	37,984
Previously impaired fixed maturity securities
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment gains	13	101
Equity securities
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment gains	0	(48,862)
Investment funds
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized investment gains	$ (1,134)	$ 1,206
AOCI Including Portion Attributable to Noncontrolling Interest \| Accounting Standards Update 2016-01
Realized and Unrealized Investment Gains Losses [Line Items]
Increase (decrease) in accumulated other comprehensive income			$ (291,000)