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	6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	$ 54,966	$ 90,853	$ 65,971
Investment securities available for sale, Recurring	974,758	619,746	638,321
Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	11,069
Purchased Non-Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	13,112	16,598	15,585
Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	12,626	38,426	19,907
Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	54,966	90,853	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] | Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	$ 11,069
Valuation Technique	Third party appraisals, Sales contracts, Broker price opinions
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	$ 13,112	$ 16,598	$ 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	$ 12,626	$ 38,426	$ 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	$ 29,228	$ 35,289	$ 30,479
Level 3 [Member] | Fair Value Measurement, Nonrecurring [Member] | Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair Value Disclosure, Nonrecurring	11,069
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	13,112	16,598	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	$ 12,626	$ 38,426	$ 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	4.00%	4.00%	0.00%
Level 3 [Member] | Minimum [Member] | Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	10.00%
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%	21.00%	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	75.00%	90.00%	50.00%
Level 3 [Member] | Maximum [Member] | Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	10.00%
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	85.00%	70.00%	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%	90.00%	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%	27.00%	20.00%
Level 3 [Member] | Average Daily Balance [Member] | Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Fair value inputs discount rate range	10.00%
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	19.00%	23.00%	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	12.00%	11.00%	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%