Securities In An Unrealized Loss Position Non-Investment Grade Fixed Maturity Securities (Details)	3 Months Ended
	Mar. 31, 2016 USD ($) position	Dec. 31, 2015 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	$ 2,757,788,000	$ 4,170,376,000
Available For Sale Equity Securities Gross Unrealized Gains	8,006,000	8,216,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	89,094,000	113,948,000
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	2,687,416,000	4,121,586,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	77,111,000	91,406,000
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	62,898,000	22,320,000
Available For Sale Equity Securities Gross Unrealized Gains	7,582,000	8,216,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	10,444,000	3,353,000
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities	7,500,000
Aggregate fair value of securities in a continuous unrealized loss position	7,474,000	26,470,000
Available For Sale Equity Securities Gross Unrealized Gains	424,000	0
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	1,539,000	19,189,000
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	290,467,000	566,793,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	6,164,000	11,308,000
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	1,438,132,000	1,281,545,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	22,846,000	14,414,000
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	381,852,000	608,633,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	4,499,000	6,269,000
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	66,950,000	188,718,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	6,461,000	12,689,000
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	441,878,000	1,309,737,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	$ 36,160,000	$ 44,393,000
Noninvestment Grade Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities	5
Noninvestment Grade Investments at Loss Less than 5 Million [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities	39
Aggregate fair value of securities in a continuous unrealized loss position	$ 176,942,000
Gross Unrealized Loss	$ 15,918,000
Noninvestment Grade Investments at Loss Less than 5 Million [Member] | Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Number of Securities	12
Aggregate fair value of securities in a continuous unrealized loss position	$ 35,540,000
Gross Unrealized Loss	$ 1,866,000
Noninvestment Grade Investments at Loss Less than 5 Million [Member] | Foreign Government Debt [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities	5
Aggregate fair value of securities in a continuous unrealized loss position	$ 22,414,000
Gross Unrealized Loss	$ 3,011,000
Noninvestment Grade Investments at Loss Less than 5 Million [Member] | Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities	15
Aggregate fair value of securities in a continuous unrealized loss position	$ 92,666,000
Gross Unrealized Loss	10,780,000
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Equity Securities Gross Unrealized Gains	$ 1,500,000
Noninvestment Grade Investments at Loss Less than 5 Million [Member] | Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities | position	7
Aggregate fair value of securities in a continuous unrealized loss position	$ 26,322,000
Gross Unrealized Loss	$ 261,000