Basis of Presentation and Accounting Policies - Valuation Methodologies for Instruments Measured at Fair Value on Nonrecurring Basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	$ 590,334	$ 688,349	$ 785,499
Impaired Loans Carried at Fair Value [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	44,754	52,514	60,277
Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	39,885	39,850	40,018
Covered Loans [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	443,517	507,712	601,737
Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	62,178	88,273	83,467
Level 3 [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	590,334	688,349	785,499
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	44,754	52,514	60,277
Level 3 [Member] | Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	39,885	39,850	40,018
Level 3 [Member] | Covered Loans [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	443,517	507,712	601,737
Level 3 [Member] | Covered Other Real Estate Owned [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Nonrecurring assets at fair value	$ 62,178	$ 88,273	$ 83,467