Supplemental Guarantor Information - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Operating activities
Income (loss) including non-controlling interests	$ (197,436)	$ (2,580)	$ (130,246)	$ 70,514
Adjustments to reconcile income (loss) including non-controlling interests to net cash provided by operating activities
Equity in earnings of subsidiaries			0	0
Share compensation expense			8,605	6,979
Interest expense on deposit liabilities			3,170	3,687
Net unrealized loss on investments and derivatives			165,202	68,107
Net realized gain on investments and derivatives			(91,712)	(184,133)
Foreign exchange gain (loss)	(746)	0	(800)	0
Amortization of premium and accretion of discount, net			478	1,031
Changes in assets and liabilities:
Reinsurance balances receivable			2,585	(65,718)
Deferred acquisition costs, net			(36,550)	(33,180)
Unearned premiums ceded			(808)	(91)
Loss and loss adjustment expenses recoverable			630	7,865
Other assets			(10,719)	(303)
Interest and dividends receivable, net			(6,452)	(2,576)
Unearned premium reserves			133,756	98,479
Loss and loss adjustment expense reserves			144,253	52,982
Accounts payable and accrued expenses			2,213	(1,935)
Reinsurance balances payable			7,916	12,133
Performance fees payable to related party			0	21,837
Increase (Decrease) in Due to Affiliates			0
Amounts due from (to) affiliates				0
Net cash provided by operating activities			191,521	55,678
Investing activities
Purchases of investments			(2,621,367)	(2,150,821)
Proceeds from sales of investments			2,274,201	1,998,673
Purchases of investments to cover short sales			(371,635)	(141,468)
Proceeds from short sales of investments			488,601	150,098
Change in due to/from brokers, net			137,054	177,516
Decrease in securities purchased under an agreement to sell			29,852	18,250
Change in restricted cash and cash equivalents			(187,121)	(68,389)
Contributed capital to subsidiaries			0
Contributed capital from parent and/or subsidiaries			0
Net cash used in investing activities			(250,415)	(16,141)
Financing activities
Proceeds from issuance of common shares, net of costs			4,334	599
Proceeds from issuance of senior notes payable, net of costs			113,220
Increase in deposit liabilities			6,975	5,782
Non-controlling interest in investment affiliate, net			(24,137)	(51,001)
Non-controlling interest in Catastrophe Fund			(59,705)	6,151
Non-controlling interest in Catastrophe Fund Manager			292	0
Dividend received by (paid to) parent			0	0
Net cash provided by (used in) financing activities			40,979	(38,469)
Net increase (decrease) in cash and cash equivalents			(17,915)	1,068
Cash and cash equivalents at beginning of period			28,734	31,625
Cash and cash equivalents at end of period	10,819	32,693	10,819	32,693
Eliminations
Operating activities
Income (loss) including non-controlling interests	212,595	4,070	135,271	(69,224)
Adjustments to reconcile income (loss) including non-controlling interests to net cash provided by operating activities
Equity in earnings of subsidiaries			(135,271)	69,224
Share compensation expense			0	0
Interest expense on deposit liabilities			0	0
Net unrealized loss on investments and derivatives			0	0
Net realized gain on investments and derivatives			0	0
Foreign exchange gain (loss)	0		0
Amortization of premium and accretion of discount, net			0	0
Changes in assets and liabilities:
Reinsurance balances receivable			0	0
Deferred acquisition costs, net			0	0
Unearned premiums ceded			0	0
Loss and loss adjustment expenses recoverable			0	0
Other assets			0	0
Interest and dividends receivable, net			0	0
Unearned premium reserves			0	0
Loss and loss adjustment expense reserves			0	0
Accounts payable and accrued expenses			0	0
Reinsurance balances payable			0	0
Performance fees payable to related party				0
Increase (Decrease) in Due to Affiliates			0
Amounts due from (to) affiliates				0
Net cash provided by operating activities			0	0
Investing activities
Purchases of investments			0	0
Proceeds from sales of investments			0	0
Purchases of investments to cover short sales			0	0
Proceeds from short sales of investments			0	0
Change in due to/from brokers, net			0	0
Decrease in securities purchased under an agreement to sell			0	0
Change in restricted cash and cash equivalents			0	0
Contributed capital to subsidiaries			425,000
Contributed capital from parent and/or subsidiaries			(425,000)
Net cash used in investing activities			0	0
Financing activities
Proceeds from issuance of common shares, net of costs			0	0
Proceeds from issuance of senior notes payable, net of costs			0
Increase in deposit liabilities			0	0
Non-controlling interest in investment affiliate, net			0	0
Non-controlling interest in Catastrophe Fund			0	0
Non-controlling interest in Catastrophe Fund Manager			0
Dividend received by (paid to) parent			0	0
Net cash provided by (used in) financing activities			0	0
Net increase (decrease) in cash and cash equivalents			0	0
Cash and cash equivalents at beginning of period			0	0
Cash and cash equivalents at end of period	0	0	0	0
Parent Guarantor | Reportable Legal Entities
Operating activities
Income (loss) including non-controlling interests	(195,715)	(5,997)	(129,583)	65,074
Adjustments to reconcile income (loss) including non-controlling interests to net cash provided by operating activities
Equity in earnings of subsidiaries			122,501	(69,224)
Share compensation expense			362	583
Interest expense on deposit liabilities			0	0
Net unrealized loss on investments and derivatives			0	0
Net realized gain on investments and derivatives			0	0
Foreign exchange gain (loss)	0		0
Amortization of premium and accretion of discount, net			0	0
Changes in assets and liabilities:
Reinsurance balances receivable			0	0
Deferred acquisition costs, net			0	0
Unearned premiums ceded			0	0
Loss and loss adjustment expenses recoverable			0	0
Other assets			(192)	(118)
Interest and dividends receivable, net			0	0
Unearned premium reserves			0	0
Loss and loss adjustment expense reserves			0	0
Accounts payable and accrued expenses			3,575	1,140
Reinsurance balances payable			0	0
Performance fees payable to related party				0
Increase (Decrease) in Due to Affiliates			1,380
Amounts due from (to) affiliates				(5,856)
Net cash provided by operating activities			(1,957)	(8,401)
Investing activities
Purchases of investments			0	0
Proceeds from sales of investments			0	0
Purchases of investments to cover short sales			0	0
Proceeds from short sales of investments			0	0
Change in due to/from brokers, net			0	0
Decrease in securities purchased under an agreement to sell			0	0
Change in restricted cash and cash equivalents			0	0
Contributed capital to subsidiaries			(158,000)
Contributed capital from parent and/or subsidiaries			0
Net cash used in investing activities			(158,000)	0
Financing activities
Proceeds from issuance of common shares, net of costs			4,334	599
Proceeds from issuance of senior notes payable, net of costs			0
Increase in deposit liabilities			0	0
Non-controlling interest in investment affiliate, net			0	0
Non-controlling interest in Catastrophe Fund			0	0
Non-controlling interest in Catastrophe Fund Manager			0
Dividend received by (paid to) parent			158,000	8,000
Net cash provided by (used in) financing activities			162,334	8,599
Net increase (decrease) in cash and cash equivalents			2,377	198
Cash and cash equivalents at beginning of period			140	294
Cash and cash equivalents at end of period	2,517	492	2,517	492
Issuer of Debt | Reportable Legal Entities
Operating activities
Income (loss) including non-controlling interests	(17,492)	0	(16,271)	0
Adjustments to reconcile income (loss) including non-controlling interests to net cash provided by operating activities
Equity in earnings of subsidiaries			12,770	0
Share compensation expense			0	0
Interest expense on deposit liabilities			0	0
Net unrealized loss on investments and derivatives			0	0
Net realized gain on investments and derivatives			0	0
Foreign exchange gain (loss)	0		0
Amortization of premium and accretion of discount, net			112	0
Changes in assets and liabilities:
Reinsurance balances receivable			0	0
Deferred acquisition costs, net			0	0
Unearned premiums ceded			0	0
Loss and loss adjustment expenses recoverable			0	0
Other assets			(1,218)	0
Interest and dividends receivable, net			1,026	0
Unearned premium reserves			0	0
Loss and loss adjustment expense reserves			0	0
Accounts payable and accrued expenses			(463)	0
Reinsurance balances payable			0	0
Performance fees payable to related party				0
Increase (Decrease) in Due to Affiliates			(173)
Amounts due from (to) affiliates				0
Net cash provided by operating activities			(4,217)	0
Investing activities
Purchases of investments			0	0
Proceeds from sales of investments			0	0
Purchases of investments to cover short sales			0	0
Proceeds from short sales of investments			0	0
Change in due to/from brokers, net			0	0
Decrease in securities purchased under an agreement to sell			0	0
Change in restricted cash and cash equivalents			0	0
Contributed capital to subsidiaries			(266,975)
Contributed capital from parent and/or subsidiaries			158,000
Net cash used in investing activities			(108,975)	0
Financing activities
Proceeds from issuance of common shares, net of costs			0	0
Proceeds from issuance of senior notes payable, net of costs			113,220
Increase in deposit liabilities			0	0
Non-controlling interest in investment affiliate, net			0	0
Non-controlling interest in Catastrophe Fund			0	0
Non-controlling interest in Catastrophe Fund Manager			0
Dividend received by (paid to) parent			0	0
Net cash provided by (used in) financing activities			113,220	0
Net increase (decrease) in cash and cash equivalents			28	0
Cash and cash equivalents at beginning of period			0	0
Cash and cash equivalents at end of period	28	0	28	0
Non-Guarantor Subsidiaries | Reportable Legal Entities
Operating activities
Income (loss) including non-controlling interests	(196,824)	(653)	(119,663)	74,664
Adjustments to reconcile income (loss) including non-controlling interests to net cash provided by operating activities
Equity in earnings of subsidiaries			0	0
Share compensation expense			8,243	6,396
Interest expense on deposit liabilities			3,170	3,687
Net unrealized loss on investments and derivatives			165,202	68,107
Net realized gain on investments and derivatives			(91,712)	(184,133)
Foreign exchange gain (loss)	(746)		(800)
Amortization of premium and accretion of discount, net			366	1,031
Changes in assets and liabilities:
Reinsurance balances receivable			2,585	(65,718)
Deferred acquisition costs, net			(36,550)	(33,180)
Unearned premiums ceded			(808)	(91)
Loss and loss adjustment expenses recoverable			630	7,865
Other assets			(9,309)	(185)
Interest and dividends receivable, net			(7,478)	(2,576)
Unearned premium reserves			133,756	98,479
Loss and loss adjustment expense reserves			144,253	52,982
Accounts payable and accrued expenses			(899)	(3,075)
Reinsurance balances payable			7,916	12,133
Performance fees payable to related party				21,837
Increase (Decrease) in Due to Affiliates			(1,207)
Amounts due from (to) affiliates				5,856
Net cash provided by operating activities			197,695	64,079
Investing activities
Purchases of investments			(2,621,367)	(2,150,821)
Proceeds from sales of investments			2,274,201	1,998,673
Purchases of investments to cover short sales			(371,635)	(141,468)
Proceeds from short sales of investments			488,601	150,098
Change in due to/from brokers, net			137,054	177,516
Decrease in securities purchased under an agreement to sell			29,852	18,250
Change in restricted cash and cash equivalents			(187,121)	(68,389)
Contributed capital to subsidiaries			(25)
Contributed capital from parent and/or subsidiaries			267,000
Net cash used in investing activities			16,560	(16,141)
Financing activities
Proceeds from issuance of common shares, net of costs			0	0
Proceeds from issuance of senior notes payable, net of costs			0
Increase in deposit liabilities			6,975	5,782
Non-controlling interest in investment affiliate, net			(24,137)	(51,001)
Non-controlling interest in Catastrophe Fund			(59,705)	6,151
Non-controlling interest in Catastrophe Fund Manager			292
Dividend received by (paid to) parent			(158,000)	(8,000)
Net cash provided by (used in) financing activities			(234,575)	(47,068)
Net increase (decrease) in cash and cash equivalents			(20,320)	870
Cash and cash equivalents at beginning of period			28,594	31,331
Cash and cash equivalents at end of period	$ 8,274	$ 32,201	$ 8,274	$ 32,201