Consolidated Statements Of Changes In Shareholders' Equity - USD ($) $ in Thousands	Total	Preference shares	Common shares	Additional paid-in capital	Accumulated other comprehensive income	Retained earnings
Beginning balance at Dec. 31, 2014		$ 400,000	$ 38,442	$ 0	$ 3,416	$ 3,423,857
Statement of Changes in Stockholders' Equity
Cumulative effect of adoption of ASU 2016-09 (Note 2)						0
Issuance of shares			7,435	754,384
Repurchase of shares			(2,473)	(257,401)
Change in redeemable noncontrolling interest				(762)
Exercise of options and issuance of restricted stock awards (Notes 12 and 17)			297	11,453
Change in net unrealized gains on investments	$ 1,308				(1,308)
Net (loss) income	542,242					542,242
Net loss (income) attributable to redeemable noncontrolling interests (Note 10)	(111,050)					(111,050)
Dividends on common shares						(53,967)
Dividends on preference shares	(22,381)					(22,381)
Ending balance at Dec. 31, 2015	4,732,184	400,000	43,701	507,674	2,108	3,778,701
Statement of Changes in Stockholders' Equity
Cumulative effect of adoption of ASU 2016-09 (Note 2)						0
Issuance of shares			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 17)			227	17,232
Change in net unrealized gains on investments	975				(975)
Net (loss) income	630,048					630,048
Net loss (income) attributable to redeemable noncontrolling interests (Note 10)	(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
Cumulative effect of adoption of ASU 2016-09 (Note 2)						2,213
Issuance of shares			0	0
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	909				(909)
Net (loss) income	(354,671)					(354,671)
Net loss (income) attributable to redeemable noncontrolling interests (Note 10)	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