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, net of deferred income tax	Common shares held in treasury, at cost
Balance at beginning of period, as adjusted					$ 9,426,299
Balance at beginning of period at Dec. 31, 2018		$ 780,000	$ 634	$ 1,793,781	9,426,299	$ (178,720)	$ (114,178)	$ (64,542)	$ (2,382,167)
Cumulative effect of an accounting change at Dec. 31, 2018					0
Common shares issued, net			2
Amortization of share-based compensation				25,908
Other changes				(84)
Net income (loss)	$ 495,498				495,498
Net (income) loss attributable to noncontrolling interests	(46,970)				(46,970)
Preferred share dividends	(10,403)				(10,403)
Unrealized holding gains (losses) during period, net of reclassification adjustment							215,666
Unrealized holding gains (losses) during period attributable to noncontrolling interests							(4,286)
Foreign currency translation adjustments	5,516							5,516
Foreign currency translation adjustments attributable to noncontrolling interests								147
Shares repurchased for treasury	(2,900)								(6,225)
Balance at end of period at Mar. 31, 2019	10,114,596	780,000	636	1,819,605	9,864,424	38,323	97,202	(58,879)	(2,388,392)
Non-redeemable noncontrolling interests, end of period at Mar. 31, 2019	838,081
Total shareholders’ equity at Mar. 31, 2019	10,952,677
Balance at beginning of period, as adjusted					10,998,554
Balance at beginning of period at Dec. 31, 2019	11,497,371	780,000	638	1,889,683	11,021,006	212,091	258,486	(46,395)	(2,406,047)
Cumulative effect of an accounting change at Dec. 31, 2019					(22,452)
Common shares issued, net			4
Amortization of share-based compensation				28,602
Other changes				3,202
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