Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Preference shares	Common shares	Additional paid-in capital	Accumulated other comprehensive (loss) income	Retained earnings
Beginning balance at Dec. 31, 2016		$ 400,000	$ 41,187	$ 216,558	$ 1,133	$ 4,207,699
Statement of Changes in Stockholders' Equity
Repurchase of shares			(1,322)	(187,269)
Change in redeemable noncontrolling interest				119
Exercise of options and issuance of restricted stock awards (Notes 12 and 17)			159	7,947
Change in net unrealized gains on investments, net of tax	$ (909)				(909)
Foreign currency translation adjustments, net of tax	0
Net income (loss)	(354,671)					(354,671)
Net (income) loss attributable to redeemable noncontrolling interests (Note 10)	132,282					132,282
Dividends on common shares	(51,400)					(51,370)
Dividends on preference shares	(22,381)					(22,381)
Ending balance at Dec. 31, 2017	4,391,375	400,000	40,024	37,355	224	3,913,772
Statement of Changes in Stockholders' Equity
Issuance of shares (Note 12)		250,000	1,947	248,053
Offering expenses				(8,552)
Change in redeemable noncontrolling interest				837
Exercise of options and issuance of restricted stock awards (Notes 12 and 17)			236	18,406
Change in net unrealized gains on investments, net of tax	(1,657)				(1,657)
Foreign currency translation adjustments, net of tax	0				0
Net income (loss)	268,917					268,917
Net (income) loss attributable to redeemable noncontrolling interests (Note 10)	(41,553)					(41,553)
Dividends on common shares	(52,800)					(52,841)
Dividends on preference shares	(30,088)					(30,088)
Ending balance at Dec. 31, 2018	5,045,080	650,000	42,207	296,099	(1,433)	4,058,207
Statement of Changes in Stockholders' Equity
Issuance of shares (Note 12)			1,739	248,259
Change in redeemable noncontrolling interest				(342)
Exercise of options and issuance of restricted stock awards (Notes 12 and 17)			202	24,261
Change in net unrealized gains on investments, net of tax	2,173				2,173
Foreign currency translation adjustments, net of tax	(2,679)				(2,679)
Net income (loss)	950,267					950,267
Net (income) loss attributable to redeemable noncontrolling interests (Note 10)	(201,469)					(201,469)
Dividends on common shares	(59,400)					(59,368)
Dividends on preference shares	(36,756)
Ending balance at Dec. 31, 2019	$ 5,971,367	$ 650,000	$ 44,148	$ 568,277	$ (1,939)	$ 4,710,881