Goodwill and Other Intangible Assets - Changes in Mortgage Servicing Rights (Detail) - Mortgage Servicing Rights [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Servicing Asset at Amortized Cost, Balance [Roll Forward]
Beginning of period	$ 5,877	$ 5,509	$ 5,519
Servicing rights capitalized	2,049	1,674	1,118
Acquired servicing rights	87	0	0
Amortization of servicing rights	(1,528)	(1,306)	(1,378)
Changes in valuation allowance	0	0	250
End of period	6,485	5,877	5,509
Mortgage loans serviced for others	$ 965,729	$ 863,947	$ 796,835