Adoption of New Accounting Standards (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014		Jun. 30, 2015	Jun. 30, 2014
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net investment income	$ 194,823	$ 189,930	[1]	$ 386,419	$ 377,981	[1]
Total revenue	1,033,694	991,036	[1]	2,056,226	2,015,207	[1]
Income before income taxes	188,388	193,811	[1]	368,820	391,349	[1]
Income taxes	(61,278)	(62,888)	[1]	(120,062)	(127,570)	[1]
Net income	$ 127,110	130,923		$ 248,758	263,779	[1]
As Previously Reported [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net investment income		182,877			363,877
Total revenue		983,983			2,001,103
Income before income taxes		186,758			377,245
Income taxes		(55,835)			(113,466)
Net income		130,923			263,779
Adjustments [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net investment income		7,053			14,104
Total revenue		7,053			14,104
Income before income taxes		7,053			14,104
Income taxes		(7,053)			(14,104)
Net income		$ 0			$ 0

[1] Certain balances were retrospectively adjusted to give effect to the adoption of new accounting guidance as described in Note G- Adoption of New Accounting Standards