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				40,381
Net income	$ 422,731				422,731
Net (income) loss attributable to noncontrolling interests	(28,662)				(28,662)
Preferred share dividends	(20,840)				(20,840)
Loss on redemption of preferred shares	(2,710)				(2,710)
Unrealized holding gains (losses) during period, net of reclassification adjustment							(152,844)
Unrealized holding gains (losses) during period attributable to noncontrolling interests							1,885
Foreign currency translation adjustments	(11,313)							(11,313)
Foreign currency translation adjustments attributable to noncontrolling interests								(135)
Shares repurchased for treasury	(173,600)								(188,788)
Balance at end of period at Jun. 30, 2018	9,163,755	780,000	633	1,760,606	9,083,202	(194,157)	(143,353)	(50,804)	(2,266,529)	0
Non-redeemable noncontrolling interests, end of period at Jun. 30, 2018	861,153
Total shareholders’ equity at Jun. 30, 2018	10,024,908
Balance at beginning of period, as adjusted					8,849,959		(96,238)
Balance at beginning of period at Mar. 31, 2018		780,000	630	1,737,978	8,849,959	(134,009)	(96,238)	(37,771)	(2,084,186)	0
Cumulative effect of an accounting change at Mar. 31, 2018					0		0
Preferred shares redeemed		0
Preferred shares converted to common shares				0						0
Common shares issued, net			3
Other changes				22,628
Net income	256,347				256,347
Net (income) loss attributable to noncontrolling interests	(12,701)				(12,701)
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							(48,628)
Unrealized holding gains (losses) during period attributable to noncontrolling interests							1,513
Foreign currency translation adjustments	(12,595)							(12,595)
Foreign currency translation adjustments attributable to noncontrolling interests								(438)
Shares repurchased for treasury									(182,343)
Balance at end of period at Jun. 30, 2018	9,163,755	780,000	633	1,760,606	9,083,202	(194,157)	(143,353)	(50,804)	(2,266,529)	0
Non-redeemable noncontrolling interests, end of period at Jun. 30, 2018	861,153
Total shareholders’ equity at Jun. 30, 2018	10,024,908
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				54,168
Net income	981,343				981,343
Net (income) loss attributable to noncontrolling interests	(63,861)				(63,861)
Preferred share dividends	(20,806)				(20,806)
Loss on redemption of preferred shares	0				0
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)	0
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, as adjusted					9,864,424		97,202
Balance at beginning of period at Mar. 31, 2019		780,000	636	1,819,605	9,864,424	38,323	97,202	(58,879)	(2,388,392)	0
Cumulative effect of an accounting change at Mar. 31, 2019					0		0
Preferred shares redeemed		0
Preferred shares converted to common shares				0						0
Common shares issued, net			2
Other changes				28,344
Net income	485,845				485,845
Net (income) loss attributable to noncontrolling interests	(16,891)				(16,891)
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							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)	$ 0
Non-redeemable noncontrolling interests, end of period at Jun. 30, 2019	855,347
Total shareholders’ equity at Jun. 30, 2019	$ 11,612,699