Loans and Allowance for Loan Losses - Loans, Net of Unearned Income (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Loans Receivable [Line Items]
Total covered loans	$ 392,002	$ 515,823
Total loans	11,734,472	11,577,802
Commercial Non-Real Estate [Member]
Loans Receivable [Line Items]
Total covered loans	24,340	29,260
Total loans	4,625,315	4,433,288
Construction and Land Development [Member]
Loans Receivable [Line Items]
Total covered loans	23,197	28,482
Total loans	920,408	989,306
Commercial Real Estate [Member]
Loans Receivable [Line Items]
Total covered loans	60,280	95,146
Total loans	2,914,969	2,923,094
Residential Mortgage Loans [Member]
Loans Receivable [Line Items]
Total covered loans	223,494	263,515
Total loans	1,695,197	1,577,944
Consumer loans [Member]
Loans Receivable [Line Items]
Total covered loans	60,691	99,420
Total loans	1,578,583	1,654,170
Originated loans [Member]
Loans Receivable [Line Items]
Total-excluding covered	8,700,767	7,107,221
Originated loans [Member] | Commercial Non-Real Estate [Member]
Loans Receivable [Line Items]
Total-excluding covered-Commercial non-real estate	3,633,490	2,713,385
Originated loans [Member] | Construction and Land Development [Member]
Loans Receivable [Line Items]
Total-excluding covered-Construction and land development	738,983	665,673
Originated loans [Member] | Commercial Real Estate [Member]
Loans Receivable [Line Items]
Total-excluding covered-Commercial real estate	1,816,402	1,548,402
Originated loans [Member] | Residential Mortgage Loans [Member]
Loans Receivable [Line Items]
Total-excluding covered-Residential mortgages	1,124,649	827,985
Originated loans [Member] | Consumer loans [Member]
Loans Receivable [Line Items]
Total-excluding covered-Consumer	1,387,243	1,351,776
Acquired loans [Member]
Loans Receivable [Line Items]
Total-excluding covered	2,641,703	3,954,758
Acquired loans [Member] | Commercial Non-Real Estate [Member]
Loans Receivable [Line Items]
Total-excluding covered-Commercial non-real estate	967,485	1,690,643
Acquired loans [Member] | Construction and Land Development [Member]
Loans Receivable [Line Items]
Total-excluding covered-Construction and land development	158,228	295,151
Acquired loans [Member] | Commercial Real Estate [Member]
Loans Receivable [Line Items]
Total-excluding covered-Commercial real estate	1,038,287	1,279,546
Acquired loans [Member] | Residential Mortgage Loans [Member]
Loans Receivable [Line Items]
Total-excluding covered-Residential mortgages	347,054	486,444
Acquired loans [Member] | Consumer loans [Member]
Loans Receivable [Line Items]
Total-excluding covered-Consumer	$ 130,649	$ 202,974