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, 2018		$ 780,000	$ 634	$ 1,793,781	$ 9,426,299	$ 0	$ 9,426,299	$ (178,720)	$ (114,178)	$ (64,542)	$ (2,382,167)
Common shares issued, net			4
Amortization of share-based compensation				39,515
Other changes				14,653
Net income (loss)	$ 981,343				981,343
Net (income) loss attributable to noncontrolling interests	(63,861)				(63,861)
Preferred share dividends	(20,806)				(20,806)
Unrealized holding gains (losses) during period, net of reclassification adjustment									382,794
Unrealized holding gains (losses) during period attributable to noncontrolling interests									(6,989)
Foreign currency translation adjustments	9,783									9,783
Foreign currency translation adjustments attributable to noncontrolling interests										(41)
Shares repurchased for treasury	(2,900)										(18,870)
Balance at end of period at Jun. 30, 2019	10,757,352	780,000	638	1,847,949	10,322,975			206,827	261,627	(54,800)	(2,401,037)
Non-redeemable noncontrolling interests, end of period at Jun. 30, 2019	855,347
Total shareholders’ equity at Jun. 30, 2019	11,612,699
Balance at beginning of period at Mar. 31, 2019		780,000	636	1,819,605	9,864,424	0	9,864,424	38,323	97,202	(58,879)	(2,388,392)
Common shares issued, net			2
Amortization of share-based compensation				13,607
Other changes				14,737
Net income (loss)	485,845				485,845
Net (income) loss attributable to noncontrolling interests	(16,891)				(16,891)
Preferred share dividends	(10,403)				(10,403)
Unrealized holding gains (losses) during period, net of reclassification adjustment									167,128
Unrealized holding gains (losses) during period attributable to noncontrolling interests									(2,703)
Foreign currency translation adjustments	4,267									4,267
Foreign currency translation adjustments attributable to noncontrolling interests										(188)
Shares repurchased for treasury											(12,645)
Balance at end of period at Jun. 30, 2019	10,757,352	780,000	638	1,847,949	10,322,975			206,827	261,627	(54,800)	(2,401,037)
Non-redeemable noncontrolling interests, end of period at Jun. 30, 2019	855,347
Total shareholders’ equity at Jun. 30, 2019	$ 11,612,699
Accounting Standards Update	us-gaap:AccountingStandardsUpdate201613Member
Balance at beginning of period at Dec. 31, 2019	$ 11,497,371	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				41,210
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	(75,500)										(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)
Common shares issued, net			0
Amortization of share-based compensation				13,160
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