Business Combinations (Summary of FDIC Indemnification Asset) (Detail) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended
	Oct. 16, 2017	Jun. 30, 2017	Jun. 30, 2017
FDIC Indemnification Asset [Roll Forward]
Balance at beginning of period		$ 18,263	$ 16,701
Reductions from reimbursable expenses		(75)	(157)
Amortization		455	699
Changes in expected reimbursements to the FDIC for changes in expected credit losses and reimbursable expenses		(3,673)	(2,659)
Payments received from the FDIC	$ 15,200	405	791
Balance at end of period		$ 15,375	$ 15,375