Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Derivative Instruments (Gain (Loss) Recognized in the Consolidated Statements of Operations Related to its Derivative Instruments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	$ (9,151)	$ 1,841	$ (13,573)	$ 66,909
Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	(9,598)	3,798	(14,368)	66,716
Not Designated as Hedging Instrument \| Net realized and unrealized (losses) gains on investments \| Interest rate futures
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	(2,767)	4,985	1,445	95,548
Not Designated as Hedging Instrument \| Net realized and unrealized (losses) gains on investments \| Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	9	243	(970)	2,852
Not Designated as Hedging Instrument \| Net realized and unrealized (losses) gains on investments \| Credit default swaps
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	366	(87)	1,790	(3,010)
Not Designated as Hedging Instrument \| Net realized and unrealized (losses) gains on investments \| Total return swaps
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	336	1,227	1,211	(5,759)
Not Designated as Hedging Instrument \| Net realized and unrealized (losses) gains on investments \| Equity futures
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	0	(4,335)	0	(30,045)
Not Designated as Hedging Instrument \| Net foreign exchange (losses) gains \| Foreign currency forward contracts, underwriting and non-investment operations
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	(11,367)	2,495	(14,768)	9,073
Not Designated as Hedging Instrument \| Net foreign exchange (losses) gains \| Foreign currency forward contracts, investment operations
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	3,825	(730)	(3,076)	(1,943)
Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	447	(1,957)	795	193
Designated as Hedging Instrument \| Foreign currency forward contracts, investment operations
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated other comprehensive loss	$ 447	$ (1,957)	$ 795	$ 193