Loans and Allowance for Loan Losses - Summary of Composition of Non-Accrual Loans by Portfolio Segment (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	$ 101,395	$ 99,657
Commercial non-real estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	17,118	13,330
Construction and land development [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	17,003	16,700
Commercial real estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	36,788	40,460
Residential mortgages [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	23,524	22,255
Consumer [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	6,962	6,912
Originated loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	76,310	74,313
Originated loans [Member] | Commercial non-real estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	13,726	10,119
Originated loans [Member] | Construction and land development [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	13,598	13,171
Originated loans [Member] | Commercial real estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	29,140	32,772
Originated loans [Member] | Residential mortgages [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	15,153	13,449
Originated loans [Member] | Consumer [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	4,693	4,802
Acquired loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	21,711	21,800
Acquired loans [Member] | Commercial non-real estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	3,391	3,209
Acquired loans [Member] | Construction and land development [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	1,866	1,990
Acquired loans [Member] | Commercial real estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	6,501	6,525
Acquired loans [Member] | Residential mortgages [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	7,971	8,262
Acquired loans [Member] | Consumer [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	1,982	1,814
Covered Loans [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	3,374	3,544
Covered Loans [Member] | Commercial non-real estate [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	1	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	1,147	1,163
Covered Loans [Member] | Residential mortgages [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	400	544
Covered Loans [Member] | Consumer [Member]
Nonaccrual Loans By Portfolio [Line Items]
Non-accrual loans	$ 287	$ 296