Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operating activities
Net income (loss)	$ 673,442	$ 1,134,514	$ (520,291)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Amortization of net premium on investments	151,666	137,313	91,339
Amortization of intangible assets	27,180	31,799	36,405
Net realized and unrealized investment losses (gains)	160,735	(493,409)	(66,692)
Changes in:
Reinsurance balances, net	(507,346)	(102,009)	(21,036)
Reinsurance recoverable on paid and unpaid losses, net of ceded premiums payable	45,422	31,730	625
Funds held by reinsured companies and funds held - directly managed	99,394	381,733	606,266
Deferred acquisition costs	(72,956)	(13,437)	52,069
Net tax assets and liabilities	(99,067)	80,628	(58,970)
Unpaid losses and loss expenses including life policy benefits	41,956	(634,736)	606,698
Unearned premiums	198,316	86,921	(161,425)
Other net changes in operating assets and liabilities	108,525	52,246	8,647
Net cash provided by operating activities	827,267	693,293	573,635
Cash flows from investing activities
Redemptions of fixed maturities	1,167,483	1,000,181	1,211,016
Payments/ proceeds from trading securities [Line Items]
Sales and redemptions of short-term investments	312,376	110,360	336,456
Purchases of short-term investments	(176,339)	(215,473)	(331,432)
Consideration paid, related to the acquisition of Presidio, net of cash acquired	0	(9,242)	0
Other, net	(786)	995	(186,823)
Net cash provided by (used in) investing activities	417,993	(219,538)	(1,080,378)
Cash flows from financing activities
Dividends paid to common and preferred shareholders	(200,078)	(217,615)	(205,784)
Repurchase of common shares	(715,421)	(504,991)	(413,737)
Issuance of common shares	51,111	34,323	16,041
Net proceeds from issuance of preferred shares	241,265	0	361,722
Redemption of preferred shares	(290,000)	0	0
Sale of shares to noncontrolling interests	47,193	0	0
Net cash used in financing activities	(865,930)	(688,283)	(241,758)
Effect of foreign exchange rate changes on cash	(4,550)	(6,024)	(20,326)
Increase (decrease) in cash and cash equivalents	374,780	(220,552)	(768,827)
Cash and cash equivalents - beginning of year	1,121,705	1,342,257	2,111,084
Cash and cash equivalents - end of year	1,496,485	1,121,705	1,342,257
Supplemental cash flow information:
Taxes paid	174,031	186,970	197,610
Interest paid	49,259	49,259	49,259
Fixed maturities [Member]
Payments/ proceeds from trading securities [Line Items]
Sales of fixed maturities and sales of equities	7,887,186	6,969,074	8,328,352
Purchases of fixed maturities and equities	(8,872,874)	(8,067,087)	(10,549,343)
Equity securities [Member]
Payments/ proceeds from trading securities [Line Items]
Sales of fixed maturities and sales of equities	796,403	821,977	730,929
Purchases of fixed maturities and equities	$ (695,456)	$ (830,323)	$ (619,533)