Reinsurance (Ceded Premiums and Losses Related to Flood Operations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Ceded premiums written	$ (93,391)	$ (86,704)	$ (180,565)	$ (164,487)
Ceded premiums earned	(86,780)	(87,157)	(172,369)	(175,365)
Ceded loss and loss expense incurred	(65,780)	(24,018)	(170,651)	(33,914)
National Flood Insurance Program [Member]
Ceded premiums written	(62,461)	(60,525)	(119,168)	(112,249)
Ceded premiums earned	(56,450)	(52,768)	(111,777)	(104,673)
Ceded loss and loss expense incurred	$ (51,725)	$ (6,754)	$ (127,901)	$ 8,168

Premiums assumed and earned by another insurer as a result of reinsurance arrangements.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 17

-Article 12

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 605

-Section 50

-Paragraph 1

-Subparagraph (b),(c)(2)

-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 605

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6486662&loc=d3e27175-158546

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 113

-Paragraph 16

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration