Investments (Details) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2015	Dec. 31, 2014
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	[1]	$ 6,505,016	$ 6,375,237
Amortized Cost/Cost, Equity securities		94,089	99,904
Unrealized Gains	[1]	438,981	543,868
Unrealized Losses	[1]	46,939	26,015
Fair Value	[1]	6,897,058	6,893,090
Fair Value, Equity securities		99,318	110,655
OTTI in AOCI	[1],[2]	(2,728)	2,879
Mortgage-backed securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	[1]	480,516	484,561
Unrealized Gains	[1]	48,405	52,555
Unrealized Losses	[1]	2,495	1,390
Fair Value	[1]	526,426	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	[1]	590,465	512,596
Unrealized Gains	[1]	21,156	28,652
Unrealized Losses	[1]	9,034	3,049
Fair Value	[1]	602,587	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]	1,511,171	1,462,717
Unrealized Gains	[1]	150,696	189,533
Unrealized Losses	[1]	13,418	4,428
Fair Value	[1]	1,648,449	1,647,822
OTTI in AOCI	[1],[2]	0	0
Foreign government bonds [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	[1]	59,500	52,552
Unrealized Gains	[1]	7,190	6,984
Unrealized Losses	[1]	0	0
Fair Value	[1]	66,690	59,536
OTTI in AOCI	[1],[2]	0	0
Corporate bonds [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	[1]	2,470,966	2,608,633
Unrealized Gains	[1]	186,773	237,372
Unrealized Losses	[1]	15,471	11,256
Fair Value	[1]	2,642,268	2,834,749
OTTI in AOCI	[1],[2]	0	0
Other mortgage-backed securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost	[1]	1,392,398	1,254,178
Unrealized Gains	[1]	24,761	28,772
Unrealized Losses	[1]	6,521	5,892
Fair Value	[1]	1,410,638	1,277,058
OTTI in AOCI	[1],[2]	(2,728)	2,879
Equity securities [Member]
Unrealized gains and losses on fixed maturities and equity securities
Amortized Cost/Cost, Equity securities	[3]	94,089	99,904
Unrealized Gains	[3]	8,565	14,159
Unrealized Losses	[3]	3,336	3,408
Fair Value, Equity securities	[3]	99,318	110,655
OTTI in AOCI	[2],[3]	$ 0	$ 0

[1] Fair value includes securities issued by Federal National Mortgage Association (“FNMA”) of $252,549 and $302,222; Federal Home Loan Mortgage Corporation (“FHLMC”) of $435,304 and $432,432; and Government National Mortgage Association (“GNMA”) of $136,356 and $137,867 as of June 30, 2015 and December 31, 2014, respectively.

[2] 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.

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