CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS’ EQUITY - USD ($) $ in Thousands		Total	Preferred Shares	Common shares (par value)	Additional paid-in capital	Accumulated other comprehensive income (loss)	Unrealized gains (losses) on available-for-sale investments, net of tax	Cumulative foreign currency translation adjustments, net of tax	Retained earnings	Treasury shares, at cost
Balance at beginning of year at Dec. 31, 2018			$ 775,000	$ 2,206	$ 2,308,583	$ (177,110)	$ (168,365)	$ (8,745)	$ 5,912,812	$ (3,791,420)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased			0
Treasury shares reissued					(21,046)					22,779
Share-based compensation expense					29,675
Unrealized gains (losses) arising during the year, net of reclassification adjustment		$ 349,886					349,886
Foreign currency translation adjustment		(1,066)						(1,066)
Net income (loss)		323,473							323,473
Preferred share dividends	[1]								(41,112)
Common share dividends	[1]								(138,487)
Shares repurchased										(10,165)
Balance at end of year at Dec. 31, 2019		5,544,008	775,000	2,206	2,317,212	171,710	181,521	(9,811)	6,056,686	(3,778,806)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased			(225,000)
Treasury shares reissued					(22,732)					24,620
Share-based compensation expense					35,574
Unrealized gains (losses) arising during the year, net of reclassification adjustment		239,114					239,114
Foreign currency translation adjustment		3,571						3,571
Net income (loss)		(120,424)							(120,424)
Preferred share dividends	[1]								(30,250)
Common share dividends	[1]								(142,405)
Shares repurchased										(10,382)
Balance at end of year at Dec. 31, 2020		5,295,694	550,000	2,206	2,330,054	414,395	420,635	(6,240)	5,763,607	(3,764,568)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased			0
Treasury shares reissued					(24,655)					25,800
Share-based compensation expense					40,780
Unrealized gains (losses) arising during the year, net of reclassification adjustment		(358,480)					(358,480)
Foreign currency translation adjustment		621						621
Net income (loss)		618,609							618,609
Preferred share dividends	[1]								(30,250)
Common share dividends	[1]								(147,221)
Shares repurchased										(10,242)
Balance at end of year at Dec. 31, 2021		$ 5,410,656	$ 550,000	$ 2,206	$ 2,346,179	$ 56,536	$ 62,155	$ (5,619)	$ 6,204,745	$ (3,749,010)

[1] Refer to Note 14 'Shareholders' Equity' for details on dividends declared and paid related to the Company's common and preferred shares.