Acquired SJB Assets and FDIC Loss Sharing Asset - Summary of Gross PCI Loans by Internal Risk Ratings by Loans (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross PCI loans	$ 74,929		$ 94,431
PCI Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross PCI loans	74,929	$ 93,712	$ 94,431
PCI Loans [Member] \| Pass [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross PCI loans	59,642	76,401
PCI Loans [Member] \| Special Mention [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross PCI loans	2,478	11,142
PCI Loans [Member] \| Substandard [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross PCI loans	12,809	6,169
PCI Loans [Member] \| Doubtful & Loss [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross PCI loans	$ 0	$ 0