Consolidated Statements of Cash Flows (USD $) In Thousands	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010
CASH FROM OPERATING ACTIVITIES:
Net income to common stockholders	$ 276,877	$ 322,436
Adjustments to reconcile net income to net cash from operating activities:
Net investment gains (losses)	(73,412)	(22,650)
Depreciation and amortization	57,332	64,063
Noncontrolling interests	(98)	238
Investment funds	(15,290)	30,879
Stock incentive plans	19,727	20,357
Change in:
Securities trading account	31,309	(6,426)
Investment in arbitrage funds	4,054	23,293
Trading account receivables from brokers and clearing organizations	(41,626)	71,036
Trading account securities sold but not yet purchased	7,477	(78,009)
Premiums and fees receivable	(111,411)	(21,559)
Due from reinsurers	(117,685)	(44,694)
Accrued investment income	4,265	(12,303)
Prepaid reinsurance premiums	(59,663)	16,780
Deferred policy acquisition costs	(45,531)	(20,819)
Deferred income taxes	27,137	19,655
Other assets	13,516	(19,716)
Reserves for losses and loss expenses	250,393	7,371
Unearned premiums	264,681	72,580
Due to reinsurers	40,156	2,630
Other liabilities	(46,965)	(34,425)
Net cash from operating activities	485,243	390,717
CASH FROM INVESTING ACTIVITIES:
Fixed maturity securities	1,129,377	1,264,497
Equity securities	112,760	79,344
Return of capital from investment funds	31,585	26,643
Proceeds from maturities and prepayments of fixed maturity securities	1,190,751	922,453
Cost of purchases, excluding trading account:
Fixed maturity securities	(2,118,556)	(1,944,374)
Equity securities	(49,932)	(123,623)
Real estate	(347,602)	0
Contributions to investment funds	(180,122)	(45,151)
Change in loans receivable	71,803	22,251
Net additions to real estate, furniture and equipment	(37,405)	(36,688)
Change in balances due to security brokers	122,447	56,129
Payment for business purchased, net of cash acquired	(8,579)	0
Net cash from investing activities	(83,473)	221,481
CASH FROM FINANCING ACTIVITIES:
Purchase of common treasury shares	(177,648)	(319,293)
Net proceeds from issuance of debt	309	305,637
Cash dividends to common stockholders	(32,272)	(30,947)
Bank deposits received	16,858	8,649
Repayments to federal home loan bank	(600)	(8,300)
Net proceeds from stock options exercised	13,757	4,720
Repayment of debt	0	(165,160)
Other, net	558	(236)
Net cash from financing activities	(179,038)	(204,930)
Net impact on cash due to change in foreign exchange rates	446	(500)
Net change in cash and cash equivalents	223,178	406,768
Cash and cash equivalents at beginning of year	642,952	515,430
Cash and cash equivalents at end of period	$ 866,130	$ 922,198

Name:	us-gaap_AdjustmentsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Entity may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Compensating balance arrangements that do not legally restrict the withdrawal or usage of cash amounts may be reported as Cash and Cash Equivalents, while legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or company statements of intention with regard to particular deposits are not generally reported as cash and cash equivalents. Includes cash and cash equivalents associated with the entity's continuing operations. Excludes cash and cash equivalents associated with the disposal group (and discontinued operation).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.1)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 1

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 7

-Footnote 1

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3044-108585

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 8, 9

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section 45

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6361293&loc=d3e6676-107765

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 7, 26

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016