Loans and Allowance for Loan Losses - Schedule of Accretable Yield of Noncovered PCI Loans, or Income Expected to be Collected (Detail) - Purchased Credit Impaired Loans [Member] - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at January 1	$ 33,603	$ 45,310
New loans purchased		3,217
Accretion of income	(7,330)	(12,990)
Reclassifications from (to) nonaccretable difference	594	5,619
Disposals/other adjustments	183	530
Balance at June 30,	$ 27,050	$ 41,686