Investments - Analysis of continual unrealized loss position (Details) (Excluding Life Funds Withheld Assets, USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Total fixed maturities and short-term investments AFS
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	$ 2,210,453	$ 2,896,210
Less than 12 months Gross Unrealized Losses	(93,830)	(61,772)
Equal to or greater than 12 months Fair Value	1,633,911	2,745,705
Equal to greater than 12 months Gross Unrealized Losses	(96,507)	(125,574)
U.S. Government and Government - Related/Supported
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	249,646	251,091
Less than 12 months Gross Unrealized Losses	(3,541)	(1,196)
Equal to or greater than 12 months Fair Value	143,891	342,890
Equal to greater than 12 months Gross Unrealized Losses	(4,619)	(5,603)
Corporate
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	688,725	1,337,470
Less than 12 months Gross Unrealized Losses	(40,874)	(33,881)
Equal to or greater than 12 months Fair Value	190,397	424,221
Equal to greater than 12 months Gross Unrealized Losses	(9,730)	(15,754)
RMBS - Agency
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	177,627	134,535
Less than 12 months Gross Unrealized Losses	(914)	(220)
Equal to or greater than 12 months Fair Value	279,354	512,652
Equal to greater than 12 months Gross Unrealized Losses	(4,858)	(10,563)
RMBS - Non-Agency
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	51,876	45,378
Less than 12 months Gross Unrealized Losses	(1,815)	(1,358)
Equal to or greater than 12 months Fair Value	188,932	202,700
Equal to greater than 12 months Gross Unrealized Losses	(16,137)	(16,797)
Commercial mortgage-backed securities
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	120,862	78,356
Less than 12 months Gross Unrealized Losses	(393)	(385)
Equal to or greater than 12 months Fair Value	109,324	169,065
Equal to greater than 12 months Gross Unrealized Losses	(3,008)	(4,877)
Collateralized debt obligations
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	92,517	249,803
Less than 12 months Gross Unrealized Losses	(294)	(2,666)
Equal to or greater than 12 months Fair Value	346,372	414,516
Equal to greater than 12 months Gross Unrealized Losses	(21,336)	(24,503)
Other asset-backed securities
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	92,193	143,044
Less than 12 months Gross Unrealized Losses	(6,219)	(2,813)
Equal to or greater than 12 months Fair Value	37,357	57,544
Equal to greater than 12 months Gross Unrealized Losses	(2,728)	(3,232)
US States and political subdivisions of the States
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	55,707	32,187
Less than 12 months Gross Unrealized Losses	(695)	(210)
Equal to or greater than 12 months Fair Value	15,310	63,695
Equal to greater than 12 months Gross Unrealized Losses	(569)	(994)
Non-U.S. Sovereign Government, Provincial, Supranational, and Government-Related/Supported
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	681,300	624,346
Less than 12 months Gross Unrealized Losses	(39,085)	(19,043)
Equal to or greater than 12 months Fair Value	322,974	558,422
Equal to greater than 12 months Gross Unrealized Losses	(33,522)	(43,251)
Equities
Fixed maturities and short-term investments - AFS:
Less than 12 months Fair Value	119,625	191,193
Less than 12 months Gross Unrealized Losses	(14,942)	(26,230)
Equal to or greater than 12 months Fair Value	0	0
Equal to greater than 12 months Gross Unrealized Losses	$ 0	$ 0