Investments (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2015	Dec. 31, 2014
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost		$ 6,676,545	$ 6,375,237
Amortized Cost/Cost, Equity securities		95,071	99,904
Unrealized Gains		454,019	543,868
Unrealized Losses		51,822	26,015
Fair Value		7,078,742	6,893,090
Fair Value, Equity securities		96,065	110,655
OTTI in AOCI	[1]	(2,744)	2,879
Mortgage-backed securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	[2]	471,128	484,561
Unrealized Gains	[2]	53,536	52,555
Unrealized Losses	[2]	984	1,390
Fair Value	[2]	523,680	535,726
OTTI in AOCI	[1],[2]	0	0
Other, including U.S. Treasury Securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	[2]	576,895	512,596
Unrealized Gains	[2]	25,349	28,652
Unrealized Losses	[2]	3,499	3,049
Fair Value	[2]	598,745	538,199
OTTI in AOCI	[1],[2]	0	0
Municipal bonds [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost		1,557,503	1,462,717
Unrealized Gains		166,315	189,533
Unrealized Losses		11,409	4,428
Fair Value		1,712,409	1,647,822
OTTI in AOCI	[1]	(4,214)	0
Foreign government bonds [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost		59,481	52,552
Unrealized Gains		7,016	6,984
Unrealized Losses		54	0
Fair Value		66,443	59,536
OTTI in AOCI	[1]	0	0
Corporate bonds [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost		2,624,263	2,608,633
Unrealized Gains		175,645	237,372
Unrealized Losses		30,271	11,256
Fair Value		2,769,637	2,834,749
OTTI in AOCI	[1]	0	0
Other mortgage-backed securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost		1,387,275	1,254,178
Unrealized Gains		26,158	28,772
Unrealized Losses		5,605	5,892
Fair Value		1,407,828	1,277,058
OTTI in AOCI	[1]	1,470	2,879
Equity securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost, Equity securities	[3]	95,071	99,904
Unrealized Gains	[3]	6,351	14,159
Unrealized Losses	[3]	5,357	3,408
Fair Value, Equity securities	[3]	96,065	110,655
OTTI in AOCI	[1],[3]	$ 0	$ 0

[1] Related to securities for which an unrealized loss was bifurcated to distinguish the credit related portion and the portion driven by other market factors. Represents the amount of other-than-temporary impairment losses in AOCI which was not included in earnings; amounts also include unrealized gains/(losses) on such impaired securities relating to changes in the fair value of those securities subsequent to the impairment measurement date.

[2] Fair value includes securities issued by Federal National Mortgage Association (“FNMA”) of $254,810 and $302,222; Federal Home Loan Mortgage Corporation (“FHLMC”) of $406,845 and $432,432; and Government National Mortgage Association (“GNMA”) of $137,291 and $137,867 as of September 30, 2015 and December 31, 2014, respectively.

[3] Includes nonredeemable (perpetual) preferred stocks, common stocks and closed-end funds.