Premises and Equipment - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014 Option Office Bank	Dec. 31, 2013	Dec. 31, 2012
Property Plant and Equipment Useful Life and Values [Abstract]
Estimated cost of construction projects in progress	$ 1,000,000	$ 1,000,000
Depreciation expense	6,642,000	4,938,000	5,032,000
Lease initial term	10 years
Number of renewal option	2
Number of bank offices	16
Number of mortgage offices	7
Rental expenses	$ 2,189,000	$ 1,777,000	$ 1,708,000