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
Series D preferred shares issued										0
Series D preferred shares converted to common shares				0						0
Common shares issued, net			4	8,265
Exercise of stock options				5,143
Amortization of share-based compensation				35,769
Other				1,426
Net income	$ 424,984				424,984
Net (income) loss attributable to noncontrolling interests	(59,131)				(59,131)
Preferred share dividends	(10,969)				(10,969)
Unrealized holding gains (losses) arising during period, net of reclassification adjustment							181,124
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	(150)						(150)
Foreign currency translation adjustments	(838)							(838)
Foreign currency translation adjustments attributable to noncontrolling interests								200
Shares repurchased for treasury									(86,786)
Balance at end of period at Jun. 30, 2016	6,665,583	325,000	581	517,942	7,686,916	163,834	231,059	(67,225)	(2,028,690)	0
Non-redeemable noncontrolling interests, end of period at Jun. 30, 2016	788,589
Total shareholders’ equity at Jun. 30, 2016	7,454,172
Net income	249,357
Net (income) loss attributable to noncontrolling interests	(38,302)
Preferred share dividends	(5,485)
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	(52)
Foreign currency translation adjustments	(18,151)
Balance at end of period at Jun. 30, 2016	6,665,583	325,000	581	517,942	7,686,916	163,834	231,059	(67,225)	(2,028,690)	0
Non-redeemable noncontrolling interests, end of period at Jun. 30, 2016	788,589
Total shareholders’ equity at Jun. 30, 2016	7,454,172
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
Series D preferred shares issued										0
Series D preferred shares converted to common shares				611,653						(611,677)
Common shares issued, net			27	9,027
Exercise of stock options				2,125
Amortization of share-based compensation				42,739
Other				(347)
Net income	473,134				473,134
Net (income) loss attributable to noncontrolling interests	(34,840)				(34,840)
Preferred share dividends	(22,567)				(22,567)
Unrealized holding gains (losses) arising during period, net of reclassification adjustment							171,493
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	0						0
Foreign currency translation adjustments	21,421							21,421
Foreign currency translation adjustments attributable to noncontrolling interests								68
Shares repurchased for treasury									(16,773)
Balance at end of period at Jun. 30, 2017	8,898,887	772,555	609	1,196,884	8,412,114	78,441	143,852	(65,411)	(2,051,343)	489,627
Non-redeemable noncontrolling interests, end of period at Jun. 30, 2017	877,456
Total shareholders’ equity at Jun. 30, 2017	9,776,343
Net income	199,099
Net (income) loss attributable to noncontrolling interests	(13,932)
Preferred share dividends	(11,349)
Portion of other-than-temporary impairment losses recognized in other comprehensive income, net of deferred income tax	0
Foreign currency translation adjustments	18,297
Balance at end of period at Jun. 30, 2017	8,898,887	$ 772,555	$ 609	$ 1,196,884	$ 8,412,114	$ 78,441	$ 143,852	$ (65,411)	$ (2,051,343)	$ 489,627
Non-redeemable noncontrolling interests, end of period at Jun. 30, 2017	877,456
Total shareholders’ equity at Jun. 30, 2017	$ 9,776,343