Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 19,467	$ 19,540
Accumulated Amortization	(10,264)	(8,905)
Net Carrying Amount	9,203	10,635
Core Deposit Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	13,198	13,198
Accumulated Amortization	(7,074)	(6,013)
Net Carrying Amount	6,124	7,185
Customer Relationship Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,699	5,699
Accumulated Amortization	(2,970)	(2,699)
Net Carrying Amount	2,729	3,000
Mortgage Servicing Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	570	643
Accumulated Amortization	(220)	(193)
Net Carrying Amount	$ 350	$ 450