Premises and Equipment, Net - Summary of premises and equipment by classification (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Property Plant And Equipment [Line Items]
Accumulated depreciation	$ (103,513)	$ (100,301)
Premises and equipment, net	126,813	121,341
Building [Member]
Property Plant And Equipment [Line Items]
Premises and Equipment, gross	$ 135,694	127,250
Building [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Lives	10 years
Building [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Lives	40 years
Furniture Fixtures And Equipment [Member]
Property Plant And Equipment [Line Items]
Premises and Equipment, gross	$ 63,436	64,734
Furniture Fixtures And Equipment [Member] | Minimum [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Lives	3 years
Furniture Fixtures And Equipment [Member] | Maximum [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Lives	15 years
Land [Member]
Property Plant And Equipment [Line Items]
Premises and Equipment, gross	$ 31,196	$ 29,658