Other Comprehensive Income (Loss) - Amounts reclassified from accumulated other comprehensive income (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses	$ (1,163)	$ (492)	$ (2,521)	$ (1,124)
Income before income taxes	437,305	282,122	1,509,006	750,436
Income tax expense	(38,116)	(33,356)	(128,474)	(78,939)
Net of tax	392,453	227,408	1,309,935	621,477
Reclassification out of accumulated other comprehensive income \| Unrealized appreciation on available-for-sale investments
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net realized gains (losses)	43,124	(23,888)	114,642	(130,409)
Other-than-temporary impairment losses	(1,163)	(492)	(2,521)	(1,124)
Income before income taxes	41,961	(24,380)	112,121	(131,533)
Income tax expense	(3,218)	1,177	(7,812)	9,226
Net of tax	$ 38,743	$ (23,203)	$ 104,309	$ (122,307)

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any gains (losses) realized during the period from the sale of investments accounted for under the cost method of accounting.

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The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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