Derivative Instruments (Details) (USD $)	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2013
Derivative offsetting [Abstract]
Derivative assets subject to master netting agreements	$ 147,700,000				$ 28,000,000
Derivative liabilities subject to master netting agreements	143,000,000				14,600,000
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments	(12,768,000)	[1]	(378,000)	[1]
Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Asset derivatives - fair value	219,059,000				39,859,000
Liability derivatives - fair value	(214,941,000)				(26,472,000)
Net derivatives - fair value	4,118,000				13,387,000
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments	(12,768,000)		(378,000)
Not Designated as Hedging Instrument [Member] | Futures contracts
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments	(9,862,000)		(829,000)
Not Designated as Hedging Instrument [Member] | Futures contracts | Other investments available for sale, at fair value
Derivative [Line Items]
Asset derivatives - fair value	469,000				461,000
Liability derivatives - fair value	(769,000)				(110,000)
Net derivatives - fair value	(300,000)				351,000
Net derivatives - notional value	1,056,045,000	[2]			475,967,000	[2]
Not Designated as Hedging Instrument [Member] | Foreign currency forward contracts
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments	(2,257,000)		(725,000)
Not Designated as Hedging Instrument [Member] | Foreign currency forward contracts | Other investments available for sale, at fair value
Derivative [Line Items]
Asset derivatives - fair value	693,000				5,023,000
Liability derivatives - fair value	(1,565,000)				(3,090,000)
Net derivatives - fair value	(872,000)				1,933,000
Net derivatives - notional value	244,614,000	[2]			330,746,000	[2]
Not Designated as Hedging Instrument [Member] | TBAs
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments	(37,000)		541,000
Not Designated as Hedging Instrument [Member] | TBAs | Fixed maturities available for sale, at fair value
Derivative [Line Items]
Asset derivatives - fair value	216,548,000				33,455,000
Liability derivatives - fair value	(211,763,000)				(21,731,000)
Net derivatives - fair value	4,785,000				11,724,000
Net derivatives - notional value	412,800,000	[2]			56,160,000	[2]
Not Designated as Hedging Instrument [Member] | Other
Net realized gains (losses) on derivative instruments
Net realized gains (losses) on derivative instruments	(612,000)		635,000
Not Designated as Hedging Instrument [Member] | Other | Other investments available for sale, at fair value
Derivative [Line Items]
Asset derivatives - fair value	1,349,000				920,000
Liability derivatives - fair value	(844,000)				(1,541,000)
Net derivatives - fair value	505,000				(621,000)
Net derivatives - notional value	$ 690,029,000	[2]			$ 347,916,000	[2]

[1] See Note 9 for information on the Company’s derivative instruments.

[2] Represents the absolute notional value of all outstanding contracts, consisting of long and short positions.