Fair Value of Financial Instruments - Summary of Significant Unobservable Inputs Used in Fair Value Measurement of Level 3 Assets and Liabilities (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	65,971	92,715
Investment securities available for sale, Recurring	638,321	554,693
Purchased Non-Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	15,585	4,276
Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	19,907	45,893
Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	65,971	92,715
Investment securities available for sale, Recurring	2,500	2,000
Level 3 [Member] | Impaired Loans Carried at Fair Value [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Valuation Technique	Third party appraisals and discounted cash flows	Third party appraisals and discounted cash flows
Level 3 [Member] | Purchased Non-Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	15,585	4,276
Valuation Technique	Third party appraisals	Third party appraisals
Level 3 [Member] | Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	19,907	45,893
Valuation Technique	Third party appraisals	Third party appraisals
Level 3 [Member] | Fair Value Measurement, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Investment securities available for sale, Recurring	2,500	2,000
Valuation Technique	Discounted par values	Discounted par values
Level 3 [Member] | Fair Value Measurement, Nonrecurring [Member] | Impaired Loans Carried at Fair Value [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	30,479	42,546
Level 3 [Member] | Fair Value Measurement, Nonrecurring [Member] | Purchased Non-Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	15,585	4,276
Level 3 [Member] | Fair Value Measurement, Nonrecurring [Member] | Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	19,907	45,893
Level 3 [Member] | Minimum [Member] | Impaired Loans Carried at Fair Value [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	0.00%	(4.00%)
Level 3 [Member] | Minimum [Member] | Purchased Non-Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	10.00%	15.00%
Level 3 [Member] | Minimum [Member] | Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	10.00%	10.00%
Level 3 [Member] | Minimum [Member] | Fair Value Measurement, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	0.00%	0.00%
Level 3 [Member] | Maximum [Member] | Impaired Loans Carried at Fair Value [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	50.00%	75.00%
Level 3 [Member] | Maximum [Member] | Purchased Non-Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	96.00%	63.00%
Level 3 [Member] | Maximum [Member] | Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	90.00%	86.00%
Level 3 [Member] | Maximum [Member] | Fair Value Measurement, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	0.00%	0.00%
Level 3 [Member] | Average Daily Balance [Member] | Impaired Loans Carried at Fair Value [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	20.00%	23.00%
Level 3 [Member] | Average Daily Balance [Member] | Purchased Non-Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	33.00%	29.00%
Level 3 [Member] | Average Daily Balance [Member] | Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	15.00%	17.00%
Level 3 [Member] | Average Daily Balance [Member] | Fair Value Measurement, Recurring [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	0.00%	0.00%