Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Cash flows from operating activities
Net income	$ 312,887	$ 234,370
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of net premium on investments	29,366	42,769
Amortization of intangible assets	7,002	7,046
Net realized and unrealized investment gains	(142,172)	(22,943)
Changes in:
Reinsurance balances, net	(581,275)	(396,018)
Reinsurance recoverable on paid and unpaid losses, net of ceded premiums payable	86,002	91,287
Funds held by reinsured companies and funds held - directly managed	17,627	6,240
Deferred acquisition costs	(79,315)	(92,334)
Net tax assets and liabilities	(33,973)	(4,928)
Unpaid losses and loss expenses including life policy benefits	13,732	(242,409)
Unearned premiums	484,712	489,751
Other net changes in operating assets and liabilities	(35,852)	1,831
Net cash provided by operating activities	78,741	114,662
Cash flows from investing activities
Redemptions of fixed maturities	180,311	259,798
Payments/ proceeds from trading securities [Line Items]
Sales and redemptions of short-term investments	15,830	99,769
Purchases of short-term investments	(31,141)	(64,147)
Other, net	13,295	43,337
Net cash (used in) provided by investing activities	(71,214)	288,943
Cash flows from financing activities
Dividends paid to common and preferred shareholders	(48,772)	(52,064)
Repurchase of common shares	(180,383)	(175,211)
Issuance of common shares, net of taxes paid	(2,581)	15,193
Net proceeds from issuance of preferred shares	0	241,265
Repurchase of preferred shares	0	(290,000)
Sale of shares to noncontrolling interests	0	36,844
Net cash used in financing activities	(231,736)	(223,973)
Effect of foreign exchange rate changes on cash	(3,239)	(14,439)
(Decrease) increase in cash and cash equivalents	(227,448)	165,193
Cash and cash equivalents - beginning of period	1,496,485	1,121,705
Cash and cash equivalents - end of period	1,269,037	1,286,898
Supplemental cash flow information:
Taxes paid	95,871	46,525
Interest paid	0	0
Fixed maturities [Member]
Payments/ proceeds from trading securities [Line Items]
Sales of fixed maturities and sales of equities	1,734,246	1,788,507
Purchases of fixed maturities and equities	(1,963,428)	(1,849,579)
Equity securities [Member]
Payments/ proceeds from trading securities [Line Items]
Sales of fixed maturities and sales of equities	9,094	156,123
Purchases of fixed maturities and equities	$ (29,421)	$ (144,865)