CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (UNAUDITED) - 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 period at Dec. 31, 2021			$ 550,000	$ 2,206	$ 2,346,179	$ 56,536	$ 62,155	$ (5,619)	$ 6,204,745	$ (3,749,010)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares reissued					(30,844)					32,389
Share-based compensation expense					39,560
Unrealized gains (losses) arising during the period, net of reclassification adjustment		$ (1,083,017)					(1,083,017)
Foreign currency translation adjustment		(16,169)						(16,169)
Net income (loss)		174,592							174,592
Preferred share dividends	[1]								(22,688)
Common share dividends	[1]								(112,381)
Shares repurchased										(48,675)
Balance at end of period at Sep. 30, 2022		4,343,423	550,000	2,206	2,354,895	(1,042,650)	(1,020,862)	(21,788)	6,244,268	(3,765,296)
Balance at beginning of period at Jun. 30, 2022			550,000	2,206	2,341,507	(724,114)	(715,077)	(9,037)	6,298,680	(3,765,648)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares reissued					(694)					694
Share-based compensation expense					14,082
Unrealized gains (losses) arising during the period, net of reclassification adjustment		(305,785)					(305,785)
Foreign currency translation adjustment		(12,751)						(12,751)
Net income (loss)		(9,384)							(9,384)
Preferred share dividends	[1]								(7,563)
Common share dividends	[1]								(37,465)
Shares repurchased										(342)
Balance at end of period at Sep. 30, 2022		4,343,423	550,000	2,206	2,354,895	(1,042,650)	(1,020,862)	(21,788)	6,244,268	(3,765,296)
Balance at beginning of period at Dec. 31, 2022		4,639,910	550,000	2,206	2,366,253	(760,300)	(743,695)	(16,605)	6,247,022	(3,765,271)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares reissued					(33,575)					35,279
Share-based compensation expense					43,000
Unrealized gains (losses) arising during the period, net of reclassification adjustment		(10,837)					(10,837)
Foreign currency translation adjustment		(4,302)						(4,302)
Net income (loss)		518,870							518,870
Preferred share dividends	[1]								(22,688)
Common share dividends	[1]								(115,025)
Shares repurchased										(17,424)
Balance at end of period at Sep. 30, 2023		5,033,208	550,000	2,206	2,375,678	(775,439)	(754,532)	(20,907)	6,628,179	(3,747,416)
Balance at beginning of period at Jun. 30, 2023			550,000	2,206	2,361,185	(630,509)	(616,552)	(13,957)	6,485,901	(3,747,822)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Treasury shares reissued					(779)					779
Share-based compensation expense					15,272
Unrealized gains (losses) arising during the period, net of reclassification adjustment		(137,980)					(137,980)
Foreign currency translation adjustment		(6,950)						(6,950)
Net income (loss)		188,098							188,098
Preferred share dividends	[1]								(7,563)
Common share dividends	[1]								(38,257)
Shares repurchased										(373)
Balance at end of period at Sep. 30, 2023		$ 5,033,208	$ 550,000	$ 2,206	$ 2,375,678	$ (775,439)	$ (754,532)	$ (20,907)	$ 6,628,179	$ (3,747,416)

[1] Refer to Note 9 'Shareholders' Equity' for details on dividends declared and paid related to the Company's common and preferred shares.