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)
Common shares issued, net			4
Amortization of share-based compensation				28,050
Other changes				3,754
Net income (loss)	$ (88,674)				(88,674)
Net (income) loss attributable to noncontrolling interests	232,791				232,791
Preferred share dividends	(10,403)				(10,403)
Unrealized holding gains (losses) during period, net of reclassification adjustment									(178,516)
Unrealized holding gains (losses) during period attributable to noncontrolling interests									33,179
Foreign currency translation adjustments	(44,689)									(44,689)
Foreign currency translation adjustments attributable to noncontrolling interests										(121)
Shares repurchased for treasury	(75,500)										(83,050)
Balance at end of period at Mar. 31, 2020	11,367,244	780,000	642	1,921,487	11,132,268			21,944	113,149	(91,205)	(2,489,097)
Non-redeemable noncontrolling interests, end of period at Mar. 31, 2020	492,785
Total shareholders’ equity at Mar. 31, 2020	11,860,029
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)
Common shares issued, net			2
Amortization of share-based compensation				40,573
Other changes				(3,626)
Net income (loss)	475,708				475,708
Net (income) loss attributable to noncontrolling interests	(37,552)				(37,552)
Preferred share dividends	(10,403)				(10,403)
Unrealized holding gains (losses) during period, net of reclassification adjustment									(259,053)
Unrealized holding gains (losses) during period attributable to noncontrolling interests									4,469
Foreign currency translation adjustments	(28,584)									(28,584)
Foreign currency translation adjustments attributable to noncontrolling interests										100
Shares repurchased for treasury	(179,300)										(191,048)
Balance at end of period at Mar. 31, 2021	13,096,472	$ 780,000	$ 645	$ 2,014,741	$ 12,790,216			$ 205,827	$ 246,711	$ (40,884)	$ (2,694,957)
Non-redeemable noncontrolling interests, end of period at Mar. 31, 2021	876,864
Total shareholders’ equity at Mar. 31, 2021	$ 13,973,336
Accounting Standards Update	us-gaap:AccountingStandardsUpdate201613Member