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	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	58,774	87,753	65,971
Investment securities available for sale, Recurring	688,132	510,934	638,321
Purchased Non-Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	13,818	3,864	15,585
Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	16,089	42,636	19,907
Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	58,774	87,753	65,971
Investment securities available for sale, Recurring	2,500	2,000	2,500
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	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	13,818	3,864	15,585
Valuation Technique	Third party appraisals	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	16,089	42,636	19,907
Valuation Technique	Third party appraisals	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	2,500
Valuation Technique	Discounted par values	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	28,867	41,253	30,479
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	13,818	3,864	15,585
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	16,089	42,636	19,907
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%	0.00%	0.00%
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%	10.00%
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%	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%	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	70.00%	75.00%	50.00%
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%	57.00%	96.00%
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	70.00%	92.00%	90.00%
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%	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	24.00%	26.00%	20.00%
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	16.00%	17.00%	20.00%
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	9.00%	12.00%	11.00%
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%	0.00%