Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities [Abstract]
Net income	$ 121,088	$ 308,253	$ 286,924
Less: Income (loss) from discontinued operations, net of tax	0	0	5,385
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Net (gains) losses on investments and other financial instruments	(3,621)	(30,751)	(35,693)
Loss on induced conversion and debt extinguishment	51,469	75,075	94,207
Deferred income tax provision	166,527	170,887	156,170
Goodwill, Impairment Loss	184,374	0	0
Amortization and impairment of other intangible assets	27,797	13,221	12,986
Depreciation, other amortization, and other impairments, net	58,038	57,795	68,639
Change in:
Accounts and notes receivable	3,628	(16,011)	25,656
Prepaid reinsurance premiums	(157,071)	(188,947)	16,800
Unearned premiums	42,716	862	35,796
Reserve for losses and LAE	(252,681)	(216,135)	(583,633)
Reinsurance funds withheld	130,397	158,001	0
Other assets	(16,491)	(7,662)	7,799
Other liabilities	4,405	57,136	(66,786)
Net cash provided by (used in) operating activities, continuing operations	360,575	381,724	13,480
Net cash provided by (used in) operating activities, discontinued operations	0	0	(1,759)
Net cash provided by (used in) operating activities	360,575	381,724	11,721
Cash flows from investing activities:
Proceeds from Sale and Maturity of Available-for-sale Securities	888,219	687,173	20,100
Proceeds from Sale of Available-for-sale Securities, Equity	38,318	74,868	146,049
Proceeds from Sale of Trading Securities Held-for-investment	194,784	290,855	78,826
Proceeds from redemptions of fixed-maturity investments available for sale	463,548	337,630	103,595
Proceeds from redemptions of fixed-maturity investments held to maturity	79,296	123,645	221,914
Purchases of Available-for-sale Securities	(1,947,916)	(1,990,652)	(1,486,318)
Purchases of equity securities available for sale	(213,469)	(830)	(75,538)
Sales, redemptions and (purchases) of short-term investments, net	324,258	334,456	222,882
Sales, redemptions and (purchases) of other assets and other invested assets, net	882	2,489	16,717
Net Cash Received (Transferred) In Sale Of Subsidiaries	(650)	0	784,866
Purchases of property and equipment, net	(28,676)	(35,542)	(25,466)
Acquisitions, net of cash acquired	(86)	(150)	(9,834)
Net cash provided by (used in) investing activities, continuing operations	(201,492)	(176,058)	(2,207)
Net cash provided by (used in) investing activities, discontinued operations	0	0	4,999
Net cash provided by (used in) investing activities	(201,492)	(176,058)	2,792
Cash flows from financing activities:
Dividends paid	(2,154)	(2,105)	(1,996)
Issuance of long-term debt, net	442,163	343,417	343,334
Purchases and redemptions of long-term debt	(593,527)	(445,072)	(156,172)
Proceeds from termination of capped calls	4,208	0	13,150
Issuance of common stock	7,132	717	1,285
Purchase of common shares	(6)	(100,188)	(202,000)
Credit facility commitment fees paid	(1,993)	0	0
Change in payable under securities lending agreements	19,357	0	0
Excess tax benefits from stock-based awards (Note 2)	0	333	3,000
Repayment of other borrowings	(264)	(371)	0
Net cash provided by (used in) financing activities, continuing operations	(125,084)	(203,269)	601
Net cash provided by (used in) financing activities, discontinued operations	0	0	0
Net cash provided by (used in) financing activities	(125,084)	(203,269)	601
Effect of exchange rate changes on cash and restricted cash	431	(481)	(133)
Increase (decrease) in cash and restricted cash	34,430	1,916	14,981
Cash and restricted cash, beginning of period	61,814	59,898	44,496
Less: Increase (decrease) in cash of business held for sale	0	0	(421)
Cash and restricted cash, end of period	96,244	61,814	59,898
Supplemental disclosures of cash flow information:
Income taxes paid (received), continuing operations	94,328	(673)	3,712
Income taxes paid, discontinued operations	0	0	2,036
Interest paid	$ 57,453	$ 65,531	$ 61,077