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
Cumulative effect of an accounting change					$ 0
Balance at beginning of year, as adjusted					7,332,032
Balance at beginning of year at Dec. 31, 2015		$ 325,000	$ 577	$ 467,339	7,332,032	$ (16,502)	$ 50,085	$ (66,587)	$ (1,941,904)	$ 0
Preferred shares issued		450,000
Preferred shares redeemed		0
Preferred shares converted to common shares				0						0
Common shares issued, net			5
Issue costs on preferred shares				(15,101)
Loss on redemption of preferred shares	$ 0			0	0
All other				63,966
Net income (loss)	728,604				728,604
Net (income) loss attributable to noncontrolling interests	(109,879)				(109,879)
Preferred share dividends	(16,453)				(16,453)
Unrealized holding gains (losses) arising during period, net of reclassification adjustment							142,413
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	(150)						(150)
Foreign currency translation adjustments	(6,150)							(6,150)
Foreign currency translation adjustments attributable to noncontrolling interests								141
Shares repurchased for treasury									(89,955)
Balance at end of period at Sep. 30, 2016	7,313,983	775,000	582	516,204	7,934,304	119,752	192,348	(72,596)	(2,031,859)	0
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2016	834,808
Total shareholders’ equity at Sep. 30, 2016	8,148,791
Loss on redemption of preferred shares	0
Net income (loss)	303,620
Net (income) loss attributable to noncontrolling interests	(50,748)
Preferred share dividends	(5,484)
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	0
Foreign currency translation adjustments	(5,312)
Balance at end of period at Sep. 30, 2016	7,313,983	775,000	582	516,204	7,934,304	119,752	192,348	(72,596)	(2,031,859)	0
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2016	834,808
Total shareholders’ equity at Sep. 30, 2016	8,148,791
Cumulative effect of an accounting change					(314)
Balance at beginning of year, as adjusted					7,996,387
Balance at beginning of year at Dec. 31, 2016	8,253,718	772,555	582	531,687	7,996,701	(114,541)	(27,641)	(86,900)	(2,034,570)	1,101,304
Preferred shares issued		230,000
Preferred shares redeemed		(230,000)
Preferred shares converted to common shares				611,653						(611,677)
Common shares issued, net			28
Issue costs on preferred shares				(7,946)
Loss on redemption of preferred shares	(6,735)			6,735	(6,735)
All other				70,831
Net income (loss)	427,917				427,917
Net (income) loss attributable to noncontrolling interests	(23,279)				(23,279)
Preferred share dividends	(34,936)				(34,936)
Unrealized holding gains (losses) arising during period, net of reclassification adjustment							214,043
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	0						0
Foreign currency translation adjustments	29,701							29,701
Foreign currency translation adjustments attributable to noncontrolling interests								479
Shares repurchased for treasury									(19,074)
Balance at end of period at Sep. 30, 2017	8,911,144	772,555	610	1,212,960	8,359,354	129,682	186,402	(56,720)	(2,053,644)	489,627
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2017	860,898
Total shareholders’ equity at Sep. 30, 2017	9,772,042
Loss on redemption of preferred shares	(6,735)
Net income (loss)	(45,217)
Net (income) loss attributable to noncontrolling interests	11,561
Preferred share dividends	(12,369)
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	0
Foreign currency translation adjustments	8,280
Balance at end of period at Sep. 30, 2017	8,911,144	$ 772,555	$ 610	$ 1,212,960	$ 8,359,354	$ 129,682	$ 186,402	$ (56,720)	$ (2,053,644)	$ 489,627
Non-redeemable noncontrolling interests, end of period at Sep. 30, 2017	860,898
Total shareholders’ equity at Sep. 30, 2017	$ 9,772,042