Goodwill and Other Intangible Assets - Summary of Amortizable Intangible Assets (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Goodwill and Intangible Assets Disclosure [Abstract]
Balance of intangible assets, Gross CDI Carrying Amount, Beginning of period	$ 31,999	$ 31,999
Additions due to acquisitions	2,090	0
Balance of intangible assets, Gross CDI Carrying Amount, End of period	34,089	31,999	31,999
Aggregate amortization expense, Gross CDI Carrying Amount	1,137	1,127	2,159
Estimated Amortization Expense, 2015	949
Estimated Amortization Expense, 2016	737
Estimated Amortization Expense, 2017	631
Estimated Amortization Expense, 2018	562
Estimated Amortization Expense, 2019	335
Estimated Amortization Expense, Thereafter	0
Balance of intangible assets, Accumulated Amortization, Beginning of period	(29,738)	(28,610)
Amortizing intangible assets, Accumulated Amortization, End of period	(30,875)	(29,738)	(28,610)
Balance of intangible assets, Net CDI Amount, Beginning of period	2,261	3,389
Balance of intangible assets, Net CDI Amount, End of period	$ 3,214	$ 2,261