Commercial Mortgage Banking - Unpaid Principal Balance of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Transfers and Servicing [Abstract]
Unpaid principal balance of loans	$ 0	$ 3,974,292

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=64830801&loc=d3e107314-111719

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