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, 2014	Dec. 31, 2013
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	$ 83,154	$ 99,657
Commercial Non-Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	11,136	13,330
Construction and Land Development [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	10,897	16,700
Commercial Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	31,749	40,460
Residential Mortgages [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	23,073	22,255
Consumer [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	6,299	6,912
Originated Loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	68,362	74,313
Originated Loans [Member] | Commercial Non-Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	9,279	10,119
Originated Loans [Member] | Construction and Land Development [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	6,083	13,171
Originated Loans [Member] | Commercial Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	26,432	32,772
Originated Loans [Member] | Residential Mortgages [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	21,326	13,449
Originated Loans [Member] | Consumer [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	5,242	4,802
Acquired Loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	11,572	21,800
Acquired Loans [Member] | Commercial Non-Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	1,857	3,209
Acquired Loans [Member] | Construction and Land Development [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	3,275	1,990
Acquired Loans [Member] | Commercial Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	4,210	6,525
Acquired Loans [Member] | Residential Mortgages [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	1,353	8,262
Acquired Loans [Member] | Consumer [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	877	1,814
Covered Loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	3,220	3,544
Covered Loans [Member] | Commercial Non-Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans		2
Covered Loans [Member] | Construction and Land Development [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	1,539	1,539
Covered Loans [Member] | Commercial Real Estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	1,107	1,163
Covered Loans [Member] | Residential Mortgages [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	394	544
Covered Loans [Member] | Consumer [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	$ 180	$ 296