Securities In An Unrealized Loss Position Non-Investment Grade Fixed Maturity Securities (Details)	6 Months Ended
	Jun. 30, 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	$ 2,114,825,000	$ 4,170,376,000
Available For Sale Equity Securities Gross Unrealized Gains	28,031,000	8,216,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	47,707,000	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	2,058,455,000	4,121,586,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	43,512,000	91,406,000
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	30,474,000	22,320,000
Available For Sale Equity Securities Gross Unrealized Gains	23,597,000	8,216,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	1,780,000	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	25,900,000
Aggregate fair value of securities in a continuous unrealized loss position	25,896,000	26,470,000
Available For Sale Equity Securities Gross Unrealized Gains	4,434,000	0
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	2,415,000	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	281,734,000	566,793,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	4,400,000	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	1,188,654,000	1,281,545,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	16,336,000	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	189,934,000	608,633,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	2,570,000	6,269,000
Foreign government
Schedule of Available-for-sale Securities [Line Items]
Aggregate fair value of securities in a continuous unrealized loss position	57,171,000	188,718,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	4,183,000	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	291,888,000	1,309,737,000
Available For Sale Securities Continuous Unrealized Loss Position Aggregate Losses Accumulated In AOCI	$ 15,341,000	$ 44,393,000
Noninvestment Grade Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities	2
Noninvestment Grade Investments at Loss Less than 5 Million [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities	33
Aggregate fair value of securities in a continuous unrealized loss position	$ 140,819,000
Gross Unrealized Loss	$ 8,503,000
Noninvestment Grade Investments at Loss Less than 5 Million [Member] | Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Number of Securities	10
Aggregate fair value of securities in a continuous unrealized loss position	$ 23,910,000
Gross Unrealized Loss	$ 1,410,000
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	7
Aggregate fair value of securities in a continuous unrealized loss position	$ 32,885,000
Gross Unrealized Loss	$ 2,003,000
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	12
Aggregate fair value of securities in a continuous unrealized loss position	$ 74,180,000
Gross Unrealized Loss	4,702,000
Common stocks
Schedule of Available-for-sale Securities [Line Items]
Available For Sale Equity Securities Gross Unrealized Gains	$ 2,400,000
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	4
Aggregate fair value of securities in a continuous unrealized loss position	$ 9,844,000
Gross Unrealized Loss	$ 388,000