Unaudited Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Non-cumulative preferred shares	Common shares	Additional paid-in capital	Retained earnings	Retained earnings Cumulative effect of an accounting change	Retained earnings Balance at beginning of period, as adjusted	Accumulated other comprehensive income (loss), net of deferred income tax	Unrealized appreciation (decline) in value of available-for-sale securities, net of deferred income tax	Foreign currency translation adjustments, net of deferred income tax	Common shares held in treasury, at cost
Balance at beginning of period at Dec. 31, 2019		$ 780,000	$ 638	$ 1,889,683	$ 11,021,006	$ (22,452)	$ 10,998,554	$ 212,091	$ 258,486	$ (46,395)	$ (2,406,047)
Preferred shares issued		0
Common shares issued, net			4
Amortization of share-based compensation				41,210
Issue costs on preferred shares				0
Other changes				4,621
Net income (loss)	$ 377,715				377,715
Net (income) loss attributable to noncontrolling interests	65,223				65,223
Preferred share dividends	(20,806)				(20,806)
Unrealized holding gains (losses) during period, net of reclassification adjustment									146,889
Unrealized holding gains (losses) during period attributable to noncontrolling interests									13,112
Foreign currency translation adjustments	(22,438)									(22,438)
Foreign currency translation adjustments attributable to noncontrolling interests										(166)
Shares repurchased for treasury											(88,458)
Balance at end of period at Jun. 30, 2020	11,991,825	780,000	642	1,935,514	11,420,686			349,488	418,487	(68,999)	(2,494,505)
Non-redeemable noncontrolling interests, end of period at Jun. 30, 2020	679,089
Total shareholders’ equity at Jun. 30, 2020	12,670,914
Balance at beginning of period at Mar. 31, 2020		780,000	642	1,921,487	11,132,268	0	11,132,268	21,944	113,149	(91,205)	(2,489,097)
Preferred shares issued		0
Common shares issued, net			0
Amortization of share-based compensation				13,160
Issue costs on preferred shares				0
Other changes				867
Net income (loss)	466,389				466,389
Net (income) loss attributable to noncontrolling interests	(167,568)				(167,568)
Preferred share dividends	(10,403)				(10,403)
Unrealized holding gains (losses) during period, net of reclassification adjustment									325,405
Unrealized holding gains (losses) during period attributable to noncontrolling interests									(20,067)
Foreign currency translation adjustments	22,251									22,251
Foreign currency translation adjustments attributable to noncontrolling interests										(45)
Shares repurchased for treasury											(5,408)
Balance at end of period at Jun. 30, 2020	11,991,825	780,000	642	1,935,514	11,420,686			349,488	418,487	(68,999)	(2,494,505)
Non-redeemable noncontrolling interests, end of period at Jun. 30, 2020	679,089
Total shareholders’ equity at Jun. 30, 2020	12,670,914
Balance at beginning of period at Dec. 31, 2020	13,105,886	780,000	643	1,977,794	12,362,463	0	12,362,463	488,895	501,295	(12,400)	(2,503,909)
Preferred shares issued		500,000
Common shares issued, net			4
Amortization of share-based compensation				57,063
Issue costs on preferred shares				(14,179)
Other changes				8,241
Net income (loss)	1,194,372				1,194,372
Net (income) loss attributable to noncontrolling interests	(80,730)				(80,730)
Preferred share dividends	(22,069)				(22,069)
Unrealized holding gains (losses) during period, net of reclassification adjustment									(241,029)
Unrealized holding gains (losses) during period attributable to noncontrolling interests									4,436
Foreign currency translation adjustments	(22,379)									(22,379)
Foreign currency translation adjustments attributable to noncontrolling interests										125
Shares repurchased for treasury											(503,669)
Balance at end of period at Jun. 30, 2021	13,986,072	1,280,000	647	2,028,919	13,454,036			230,048	264,702	(34,654)	(3,007,578)
Non-redeemable noncontrolling interests, end of period at Jun. 30, 2021	918,874
Total shareholders’ equity at Jun. 30, 2021	$ 14,904,946
Accounting Standards Update	us-gaap:AccountingStandardsUpdate201613Member
Balance at beginning of period at Mar. 31, 2021		780,000	645	2,014,741	12,790,216	$ 0	$ 12,790,216	205,827	246,711	(40,884)	(2,694,957)
Preferred shares issued		500,000
Common shares issued, net			2
Amortization of share-based compensation				16,490
Issue costs on preferred shares				(14,179)
Other changes				11,867
Net income (loss)	$ 718,664				718,664
Net (income) loss attributable to noncontrolling interests	(43,178)				(43,178)
Preferred share dividends	(11,666)				(11,666)
Unrealized holding gains (losses) during period, net of reclassification adjustment									18,024
Unrealized holding gains (losses) during period attributable to noncontrolling interests									(33)
Foreign currency translation adjustments	6,205									6,205
Foreign currency translation adjustments attributable to noncontrolling interests										25
Shares repurchased for treasury											(312,621)
Balance at end of period at Jun. 30, 2021	13,986,072	$ 1,280,000	$ 647	$ 2,028,919	$ 13,454,036			$ 230,048	$ 264,702	$ (34,654)	$ (3,007,578)
Non-redeemable noncontrolling interests, end of period at Jun. 30, 2021	918,874
Total shareholders’ equity at Jun. 30, 2021	$ 14,904,946