Loans and Allowance for Loan Losses - Summary of Composition of Non-Accrual Loans by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	$ 119,708	$ 137,615
Commercial Non-Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	17,502	23,267
Construction and Land Development [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	24,466	41,231
Commercial Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	46,997	48,019
Residential Mortgage Loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	23,754	18,649
Consumer loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	6,989	6,449
Originated loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	91,462	103,428
Originated loans [Member] | Commercial Non-Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	14,118	18,941
Originated loans [Member] | Construction and Land Development [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	19,817	32,777
Originated loans [Member] | Commercial Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	39,695	40,190
Originated loans [Member] | Residential Mortgage Loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	13,148	7,705
Originated loans [Member] | Consumer loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	4,684	3,815
Acquired loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	23,083	30,087
Acquired loans [Member] | Commercial Non-Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	3,381	4,326
Acquired loans [Member] | Construction and Land Development [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	2,025	5,967
Acquired loans [Member] | Commercial Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	6,123	6,609
Acquired loans [Member] | Residential Mortgage Loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	9,664	10,551
Acquired loans [Member] | Consumer loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	1,890	2,634
Covered loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	5,163	4,100
Covered loans [Member] | Commercial Non-Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	3
Covered loans [Member] | Construction and Land Development [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	2,624	2,487
Covered loans [Member] | Commercial Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	1,179	1,220
Covered loans [Member] | Residential Mortgage Loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	942	393
Covered loans [Member] | Consumer loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-Accrual Loans	$ 415