Premises and Equipment, Net and Other Assets - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property Plant And Equipment [Abstract]
Percentage of equity investment	50.00%
Low income housing tax credit investments	$ 15.2	$ 14.5
Tax credits and other tax benefits recognized from LIHTC investments	4.2	4.0	$ 3.3
Amortization expense resulting from LIHTC investments	2.9	$ 2.6	$ 2.3
Unfunded commitment on investments	$ 13.5