Realized and Unrealized Investment Gains and Losses (Change in Unrealized Gains (Losses) of Available For Sales Securities) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018	Dec. 31, 2016
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized gains (losses) before income taxes and noncontrolling interests	$ 261,970,000	$ (302,737,000)	$ (69,425,000)
Income tax (expense) benefit	(46,068,000)	50,410,000	17,673,000
Noncontrolling interests	103,000	(46,000)	19,000
Total change in unrealized gains and losses	216,005,000	(252,373,000)	(51,733,000)
Investment funds	(2,825,000)	(212,000)	125,423,000
Other-than-temporary impairments	0	5,687,000	0
Retained earnings
Realized and Unrealized Investment Gains Losses [Line Items]
Cumulative effect adjustment resulting from changes in accounting principles		0	215,939,000		$ 0
Accounting Standards Update 2016-01 | Retained earnings
Realized and Unrealized Investment Gains Losses [Line Items]
Cumulative effect adjustment resulting from changes in accounting principles				$ 291,000,000
Fixed maturity securities
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized gains (losses) before income taxes and noncontrolling interests	271,825,000	(297,084,000)	(2,192,000)
Other-than-temporary impairments		6,000,000
Previously impaired fixed maturity securities
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized gains (losses) before income taxes and noncontrolling interests	369,000	(132,000)	895,000
Equity securities
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized gains (losses) before income taxes and noncontrolling interests	0	0	(77,971,000)
Investment funds
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized gains (losses) before income taxes and noncontrolling interests	(2,299,000)	(5,672,000)	10,179,000
Other
Realized and Unrealized Investment Gains Losses [Line Items]
Total change in unrealized gains (losses) before income taxes and noncontrolling interests	$ (7,925,000)	$ 151,000	(336,000)
Office Building in Washington, D.C.
Realized and Unrealized Investment Gains Losses [Line Items]
Investment funds			$ 124,000,000