Business Combinations (Summary of FDIC Indemnification Asset) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
FDIC Indemnification Asset [Roll Forward]
Balance at beginning of period	$ 15,375	$ 11,729	$ 16,701	$ 6,100
Reductions from reimbursable expenses	(159)	(21)	(316)	(751)
Amortization	311	456	1,010	1,322
Changes in expected reimbursements from (to) the FDIC for changes in expected credit losses and reimbursable expenses	994	4,077	(1,665)	9,150
Payments (paid to) received from the FDIC	(1,049)	1,704	(258)	2,124
Balance at end of period	$ 15,472	$ 17,945	$ 15,472	$ 17,945