Fair Value of Financial Instruments - Assets Measured at Fair Value on Nonrecurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	$ 113,697	$ 126,066	$ 136,094
Impaired Loans Carried at Fair Value [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	35,834	42,546	43,564
Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	35,320	33,351	39,978
Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	28,883	45,893	52,552
Purchased Non-Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	13,660	4,276
Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	113,697	126,066	136,094
Level 3 [Member] | Impaired Loans Carried at Fair Value [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	35,834	42,546	43,564
Level 3 [Member] | Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	35,320	33,351	39,978
Level 3 [Member] | Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	28,883	45,893	52,552
Level 3 [Member] | Purchased Non-Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	$ 13,660	$ 4,276