Borrowings (Details Textual) (USD $)	Dec. 31, 2012
Put Option [Member]
Borrowings (Textual)
FHLB advances	$ 275,000,000
Minimum rate to exercise put option	8.00%
Unsecured Debt [Member]
Borrowings (Textual)
Unsecured lines of credit	$ 171,000,000

Amount borrowed under the credit facility as of the balance sheet date.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

Name:	us-gaap_LineOfCreditFacilityAmountOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant