Fair Value - Fair Value Option for Newly Originated Permanent Construction Loans Held for Sale (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value Inputs Assets Quantitative Information [Line Items]
Aggregate fair value	$ 83,541	$ 62,593
Construction [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Aggregate fair value	83,541	62,593
Contractual balance	79,898	62,843
Gain (loss)	$ 3,643	$ (250)

For loans held as assets for which the fair value option has been elected, this item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of those loans that are 90 days or more past due, in nonaccrual status, or both.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (e)(3)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

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