Business Combinations - Schedule of Cost Basis, Fair Value Discount and Loan Acquired (Detail) - North Valley Bancorp [Member] $ in Thousands	Oct. 03, 2014 USD ($)
Business Acquisition [Line Items]
Cost Basis	$ 514,125
Discount	(14,798)
Fair Value	499,327
PNCI [Member]
Business Acquisition [Line Items]
Cost Basis	502,637
Discount	(12,721)
Fair Value	489,916
PCI - Other [Member]
Business Acquisition [Line Items]
Cost Basis	11,488
Discount	(2,077)
Fair Value	$ 9,411