Loans Receivable and Allowance for Loan Losses - Schedule of FDIC Loss Sharing Receivable (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
FDIC Indemnification Asset [Roll Forward]
Beginning Balance	$ 0	$ (2,083)	$ 2,320
Increased (decreased) estimated cash flows	0	289	(3,872)
Increased estimated cash flows from covered OREO	0	0	3,138
Other activity, net	0	(255)	248
Cash receipts from FDIC	0	2,049	(3,917)
Ending Balance	0	0	(2,083)
Provision for loan losses	6,768	3,330	16,694
Effect attributable to FDIC loss sharing arrangements	0	(289)	3,872
Net amount reported as provision for loan losses	$ 6,768	$ 3,041	$ 20,566