Loans Held for Investment by Credit Risk Category (Parenthetical) (Detail) - Watchlist - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable Recorded Investment [Line Items]
Total Impaired Loans	$ 128,467	$ 126,478
Loans not impaired	$ 22,440	$ 22,300

Recorded Investment in financing receivables that are past due at the balance sheet date.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953401-111524

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