Goodwill and Other Intangible Assets - Changes in Servicing Rights (Detail) - Servicing Rights [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Servicing Asset at Amortized Cost, Balance [Roll Forward]
Beginning of period	$ 6,485	$ 5,877	$ 5,509
Servicing rights capitalized	1,487	2,049	1,674
Acquired servicing rights	0	87	0
Amortization of servicing rights	(1,399)	(1,528)	(1,306)
Changes in valuation allowance	0	0	0
End of period	6,573	6,485	5,877
Residential mortgage and SBA loans serviced for others	$ 1,008,123	$ 965,729	$ 863,947