Fair Value Measurement - Fair Value Option for Newly Originated Residential Mortgage and Permanent Construction Loans Held for Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value Inputs Assets Quantitative Information [Line Items]
Aggregate fair value	$ 107,701	$ 83,541
Construction [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Aggregate fair value	107,701	83,541
Contractual balance	106,255	79,898
Gain	$ 1,446	$ 3,643

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