Business Combinations (Summary of FDIC Indemnification Asset) (Detail) - USD ($) $ in Thousands		3 Months Ended	9 Months Ended
	Oct. 16, 2017	Sep. 30, 2017	Sep. 30, 2017
FDIC Indemnification Asset [Roll Forward]
Balance at beginning of period		$ 15,375	$ 16,701
Reductions from reimbursable expenses		(159)	(316)
Amortization		311	1,010
Changes in expected reimbursements to the FDIC for changes in expected credit losses and reimbursable expenses		994	(1,665)
Payments received from the FDIC	$ 15,200	(1,049)	(258)
Balance at end of period		$ 15,472	$ 15,472