Derivatives (Details 11) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Losses located for swaptions
Interest expense	$ 25,256	$ 19,865	$ 20,688
Swaptions [Member]
Losses located for swaptions
Interest expense	$ (328)	$ 0

Amount of net interest income or expense derived from banking operations.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 10

-Article 9

Name:	us-gaap_InterestIncomeExpenseNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration