Loans and Allowance for Loan Losses - Schedule of Accretable Yield of Noncovered PCI Loans, or Income Expected to be Collected (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Allowance for Credit Losses [Line Items]
Accretion of income	$ (12,300)	$ (15,200)
Purchased Credit Impaired Loans [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Balance at beginning of period	27,835	33,603	$ 45,310
New loans purchased	2,384	1,556	3,217
Accretion of income	(12,252)	(15,217)	(23,447)
Reclassifications from (to) nonaccretable difference	6,133	7,614	10,589
Disposals/other adjustments	951	279	(2,066)
Balance at end of period	$ 25,051	$ 27,835	$ 33,603