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, 2015		$ 400,000	$ 43,701	$ 507,674	$ 2,108	$ 3,778,701
Statement of Changes in Stockholders' Equity
Issuance of shares (Note 11)		0	0	0
Repurchase of shares			(2,741)	(306,693)
Change in redeemable noncontrolling interest				(1,655)
Exercise of options and issuance of restricted stock awards (Notes 12 and 16)			227	17,232
Change in net unrealized (losses) gains on investments	$ 975				(975)
Net income (loss)	630,048					630,048
Net (income) loss attributable to redeemable noncontrolling interests (Note 9)	(127,086)					(127,086)
Dividends on common shares						(51,583)
Dividends on preference shares	(22,381)					(22,381)
Ending balance at Dec. 31, 2016	4,866,577	400,000	41,187	216,558	1,133	4,207,699
Statement of Changes in Stockholders' Equity
Issuance of shares (Note 11)		0	0	0
Repurchase of shares			(1,322)	(187,269)
Offering expenses				0
Change in redeemable noncontrolling interest				119
Exercise of options and issuance of restricted stock awards (Notes 12 and 16)			159	7,947
Change in net unrealized (losses) gains on investments	909				(909)
Net income (loss)	(354,671)					(354,671)
Net (income) loss attributable to redeemable noncontrolling interests (Note 9)	132,282					132,282
Dividends on common shares						(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 11)		250,000	1,947	248,053
Repurchase of shares			0	0
Offering expenses				(8,552)
Change in redeemable noncontrolling interest				837
Exercise of options and issuance of restricted stock awards (Notes 12 and 16)			236	18,406
Change in net unrealized (losses) gains on investments	1,657				(1,657)
Net income (loss)	268,917					268,917
Net (income) loss attributable to redeemable noncontrolling interests (Note 9)	(41,553)					(41,553)
Dividends on common shares						(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