Loans - Major Classes of Loans (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Commercial, financial and agricultural:
Total commercial, financial & agricultural	$ 5,290,244	$ 5,353,991
Residential real estate	2,248,037	2,263,354
Construction & land development	1,162,742	1,133,251
Consumer:
Bankcard	10,428	10,437
Other consumer	385,850	358,459
Total Financing Receivables	9,097,301	9,119,492
Owner-Occupied [Member]
Commercial, financial and agricultural:
Total commercial, financial & agricultural	962,615	1,016,364
Consumer:
Total Financing Receivables	962,615	1,016,364
Nonowner-Occupied [Member]
Commercial, financial and agricultural:
Total commercial, financial & agricultural	2,719,910	2,760,189
Consumer:
Total Financing Receivables	2,719,910	2,760,189
Other Commercial Loans [Member]
Commercial, financial and agricultural:
Total commercial, financial & agricultural	$ 1,607,719	$ 1,577,438