Unaudited Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Non-cumulative preferred shares	Common shares	Additional paid-in capital	Retained earnings	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	Common shares held in treasury, at cost	Convertible non-voting common equivalent preferred shares
Balance at beginning of period, as adjusted					$ 8,712,683		$ 7,606
Balance at beginning of period at Dec. 31, 2017		$ 872,555	$ 611	$ 1,230,617	8,562,889	$ 118,044	157,400	$ (39,356)	$ (2,077,741)	$ 489,627
Cumulative effect of an accounting change at Dec. 31, 2017					149,794		(149,794)
Preferred shares redeemed		(92,555)
Preferred shares converted to common shares				489,608						(489,627)
Common shares issued, net			22
Other changes				55,274
Net income	$ 671,497				671,497
Net (income) loss attributable to noncontrolling interests	(50,020)				(50,020)
Preferred share dividends	(31,242)				(31,242)
Loss on redemption of preferred shares	(2,710)				(2,710)
Unrealized holding gains (losses) during period, net of reclassification adjustment							(182,949)
Unrealized holding gains (losses) during period attributable to noncontrolling interests							3,123
Foreign currency translation adjustments	(9,250)							(9,250)
Foreign currency translation adjustments attributable to noncontrolling interests								(215)
Shares repurchased for treasury	(184,500)								(202,410)
Balance at end of period at Sep. 30, 2018	9,355,148	780,000	633	1,775,499	9,300,208	(221,041)	(172,220)	(48,821)	(2,280,151)	0
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2018	876,754
Total shareholders’ equity at Sep. 30, 2018	10,231,902
Balance at beginning of period, as adjusted					9,083,202		(143,353)
Balance at beginning of period at Jun. 30, 2018		780,000	633	1,760,606	9,083,202	(194,157)	(143,353)	(50,804)	(2,266,529)	0
Cumulative effect of an accounting change at Jun. 30, 2018					0		0
Preferred shares redeemed		0
Preferred shares converted to common shares				0						0
Common shares issued, net			0
Other changes				14,893
Net income	248,766				248,766
Net (income) loss attributable to noncontrolling interests	(21,358)				(21,358)
Preferred share dividends	(10,402)				(10,402)
Loss on redemption of preferred shares	0				0
Unrealized holding gains (losses) during period, net of reclassification adjustment							(30,105)
Unrealized holding gains (losses) during period attributable to noncontrolling interests							1,238
Foreign currency translation adjustments	2,063							2,063
Foreign currency translation adjustments attributable to noncontrolling interests								(80)
Shares repurchased for treasury									(13,622)
Balance at end of period at Sep. 30, 2018	9,355,148	780,000	633	1,775,499	9,300,208	(221,041)	(172,220)	(48,821)	(2,280,151)	0
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2018	876,754
Total shareholders’ equity at Sep. 30, 2018	10,231,902
Balance at beginning of period, as adjusted					9,426,299		(114,178)
Balance at beginning of period at Dec. 31, 2018	9,439,827	780,000	634	1,793,781	9,426,299	(178,720)	(114,178)	(64,542)	(2,382,167)	0
Cumulative effect of an accounting change at Dec. 31, 2018					0		0
Preferred shares redeemed		0
Preferred shares converted to common shares				0						0
Common shares issued, net			4
Other changes				70,687
Net income	1,380,532				1,380,532
Net (income) loss attributable to noncontrolling interests	(70,597)				(70,597)
Preferred share dividends	(31,209)				(31,209)
Loss on redemption of preferred shares	0				0
Unrealized holding gains (losses) during period, net of reclassification adjustment							403,341
Unrealized holding gains (losses) during period attributable to noncontrolling interests							(5,970)
Foreign currency translation adjustments	(6,641)							(6,641)
Foreign currency translation adjustments attributable to noncontrolling interests								(296)
Shares repurchased for treasury	(2,900)								(21,582)
Balance at end of period at Sep. 30, 2019	11,158,096	780,000	638	1,864,468	10,705,025	211,714	283,193	(71,479)	(2,403,749)	0
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2019	854,924
Total shareholders’ equity at Sep. 30, 2019	12,013,020
Balance at beginning of period, as adjusted					10,322,975		261,627
Balance at beginning of period at Jun. 30, 2019		780,000	638	1,847,949	10,322,975	206,827	261,627	(54,800)	(2,401,037)	0
Cumulative effect of an accounting change at Jun. 30, 2019					0		0
Preferred shares redeemed		0
Preferred shares converted to common shares				0						0
Common shares issued, net			0
Other changes				16,519
Net income	399,189				399,189
Net (income) loss attributable to noncontrolling interests	(6,736)				(6,736)
Preferred share dividends	(10,403)				(10,403)
Loss on redemption of preferred shares	0				0
Unrealized holding gains (losses) during period, net of reclassification adjustment							20,547
Unrealized holding gains (losses) during period attributable to noncontrolling interests							1,019
Foreign currency translation adjustments	(16,424)							(16,424)
Foreign currency translation adjustments attributable to noncontrolling interests								(255)
Shares repurchased for treasury									(2,712)
Balance at end of period at Sep. 30, 2019	11,158,096	$ 780,000	$ 638	$ 1,864,468	$ 10,705,025	$ 211,714	$ 283,193	$ (71,479)	$ (2,403,749)	$ 0
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2019	854,924
Total shareholders’ equity at Sep. 30, 2019	$ 12,013,020