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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	$ (8,492)	$ 14,973	$ (4,422)	$ 65,068
Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	(10,929)	23,667	(4,770)	62,918
Not Designated as Hedging Instrument \| Net realized and unrealized gains (losses) on investments \| Interest rate futures
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	(11,295)	2,557	4,212	90,563
Not Designated as Hedging Instrument \| Net realized and unrealized gains (losses) on investments \| Interest rate swaps
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	(78)	502	(979)	2,609
Not Designated as Hedging Instrument \| Net realized and unrealized gains (losses) on investments \| Credit default swaps
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	1,169	1,974	1,424	(2,923)
Not Designated as Hedging Instrument \| Net realized and unrealized gains (losses) on investments \| Total return swaps
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	875	14,151	875	(6,986)
Not Designated as Hedging Instrument \| Net realized and unrealized gains (losses) on investments \| Equity futures
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	0	5,188	0	(25,710)
Not Designated as Hedging Instrument \| Net foreign exchange gains (losses) \| Foreign currency forward contracts, underwriting and non-investment operations
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	240	6,908	(3,401)	6,578
Not Designated as Hedging Instrument \| Net foreign exchange gains (losses) \| Foreign currency forward contracts, investment operations
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	(1,840)	(7,613)	(6,901)	(1,213)
Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Amount of gain (loss) recognized on derivatives	2,437	(8,694)	348	2,150
Designated as Hedging Instrument \| Foreign currency forward contracts, investment operations
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated other comprehensive loss	$ 2,437	$ (8,694)	$ 348	$ 2,150