Commercial Mortgage Banking - Unpaid Principal Balance of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Transfers and Servicing [Abstract]
Unpaid principal balance of loans	$ 4,090,937	$ 4,134,894

This is the sum of principal amount outstanding for both securitized and unsecuritized loans of all types.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=51814546&loc=d3e107314-111719

Name:	us-gaap_PrincipalAmountOutstandingOnLoansManagedAndSecuritized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant