CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (UNAUDITED) - USD ($) $ in Thousands		Total	Preferred shares	Common shares	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, 2019			$ 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					(19,151)					21,040
Share-based compensation expense					19,293
Unrealized gains (losses) arising during the period, net of reclassification adjustment		$ 113,780					113,780
Foreign currency translation adjustment		(3,891)						(3,891)
Net income (loss)		(57,783)							(57,783)
Preferred share dividends	[1]								(15,125)
Common share dividends	[1]								(70,749)
Shares repurchased										(8,602)
Balance at end of period at Jun. 30, 2020		5,297,820	550,000	2,206	2,317,354	281,599	295,301	(13,702)	5,913,029	(3,766,368)
Balance at beginning of period at Mar. 31, 2020			550,000	2,206	2,307,998	(89,919)	(72,383)	(17,536)	5,836,007	(3,766,714)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased			0
Treasury shares reissued					(456)					456
Share-based compensation expense					9,812
Unrealized gains (losses) arising during the period, net of reclassification adjustment		367,684					367,684
Foreign currency translation adjustment		3,834						3,834
Net income (loss)		120,040							120,040
Preferred share dividends	[1]								(7,563)
Common share dividends	[1]								(35,455)
Shares repurchased										(110)
Balance at end of period at Jun. 30, 2020		5,297,820	550,000	2,206	2,317,354	281,599	295,301	(13,702)	5,913,029	(3,766,368)
Balance at beginning of period 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					(24,040)					25,185
Share-based compensation expense					20,274
Unrealized gains (losses) arising during the period, net of reclassification adjustment		(192,809)					(192,809)
Foreign currency translation adjustment		4,731						4,731
Net income (loss)		358,770							358,770
Preferred share dividends	[1]								(15,125)
Common share dividends	[1]								(73,101)
Shares repurchased										(9,819)
Balance at end of period at Jun. 30, 2021		5,389,760	550,000	2,206	2,326,288	226,317	227,826	(1,509)	6,034,151	(3,749,202)
Balance at beginning of period at Mar. 31, 2021			550,000	2,206	2,316,147	214,861	219,852	(4,991)	5,842,850	(3,749,674)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares repurchased			0
Treasury shares reissued					(911)					911
Share-based compensation expense					11,052
Unrealized gains (losses) arising during the period, net of reclassification adjustment		7,974					7,974
Foreign currency translation adjustment		3,482						3,482
Net income (loss)		235,473							235,473
Preferred share dividends	[1]								(7,563)
Common share dividends	[1]								(36,609)
Shares repurchased										(439)
Balance at end of period at Jun. 30, 2021		$ 5,389,760	$ 550,000	$ 2,206	$ 2,326,288	$ 226,317	$ 227,826	$ (1,509)	$ 6,034,151	$ (3,749,202)

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