Loans and Allowance for Loan Losses - Loans, Net of Unearned Income (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Loans Receivable [Line Items]
Total covered loans	$ 280,830	$ 358,666
Total loans	13,348,574	12,324,817
Commercial Non-Real Estate [Member]
Loans Receivable [Line Items]
Total covered loans	11,171	23,390
Total loans	5,587,137	5,064,224
Construction and Land Development [Member]
Loans Receivable [Line Items]
Total covered loans	11,166	20,229
Total loans	1,095,902	915,541
Commercial Real Estate [Member]
Loans Receivable [Line Items]
Total covered loans	41,550	53,165
Total loans	3,100,834	3,042,841
Residential Mortgages [Member]
Loans Receivable [Line Items]
Total covered loans	185,289	209,018
Total loans	1,858,490	1,720,614
Consumer [Member]
Loans Receivable [Line Items]
Total covered loans	31,654	52,864
Total loans	1,706,211	1,581,597
Originated Loans [Member]
Loans Receivable [Line Items]
Ending balance: Loans	11,285,568	9,494,132
Originated Loans [Member] | Commercial Non-Real Estate [Member]
Loans Receivable [Line Items]
Total Commercial non-real estate	4,806,740	4,113,837
Originated Loans [Member] | Construction and Land Development [Member]
Loans Receivable [Line Items]
Total Construction and land development	974,442	752,381
Originated Loans [Member] | Commercial Real Estate [Member]
Loans Receivable [Line Items]
Total Commercial real estate	2,245,855	2,022,528
Originated Loans [Member] | Residential Mortgages [Member]
Loans Receivable [Line Items]
Total Residential mortgages	1,635,462	1,196,256
Originated Loans [Member] | Consumer [Member]
Loans Receivable [Line Items]
Total Consumer	1,623,069	1,409,130
Acquired Loans [Member]
Loans Receivable [Line Items]
Ending balance: Loans	1,782,176	2,472,019
Acquired Loans [Member] | Commercial Non-Real Estate [Member]
Loans Receivable [Line Items]
Total Commercial non-real estate	769,226	926,997
Acquired Loans [Member] | Construction and Land Development [Member]
Loans Receivable [Line Items]
Total Construction and land development	110,294	142,931
Acquired Loans [Member] | Commercial Real Estate [Member]
Loans Receivable [Line Items]
Total Commercial real estate	813,429	967,148
Acquired Loans [Member] | Residential Mortgages [Member]
Loans Receivable [Line Items]
Total Residential mortgages	37,739	315,340
Acquired Loans [Member] | Consumer [Member]
Loans Receivable [Line Items]
Total Consumer	$ 51,488	$ 119,603