Premises and Equipment - Summary of Premises and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 68,208	$ 57,348
Less: accumulated depreciation	32,830	25,759
Premises and equipment, net	35,378	31,589
Land [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	4,726	4,412
Premises and Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	35,839	28,764
Furniture, Fixtures and Equipment [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	24,137	20,248
Construction in Process [Member]
Property, Plant and Equipment [Line Items]
Premises and equipment, gross	$ 3,506	$ 3,924