Note Guarantees (Other Guarantees) - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Guarantor Obligations [Line Items]
Funds Advanced To Investors Under Servicing Agreements	$ 107,299	$ 69,711
Financial Standby Letter Of Credit
Guarantor Obligations [Line Items]
Guarantees, unamortized balance of the obligations	$ 300	$ 300

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248

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