Acquisitions - Additional Information (Detail) (USD $)	12 Months Ended						12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jun. 04, 2011	Dec. 31, 2011 Mississippi Gulf Coast [Member] Branch	Dec. 31, 2011 Bogalusa La [Member] Branch	Dec. 31, 2011 Common Stock [Member]	Jun. 04, 2011 Common Stock [Member]	Dec. 31, 2012 Whitney [Member]	Dec. 31, 2011 Whitney [Member]	Dec. 31, 2010 Whitney [Member]	Sep. 16, 2011 Whitney Bank Divested Branches [Member]
Business Acquisition [Line Items]
Shares in Hancock for each share of Whitney							0.418
Business acquisition, number of shares issued		40,794,261
Business acquisition, fair value of shares issued								$ 1,300,000,000
TARP stock redeemed				307,700,000
Business acquisition, total purchase price				1,600,000,000
Number of bank branches divested					7	1
Loans	11,595,512,000	11,191,901,000										47,000,000
Deposits	15,744,188,000	15,713,579,000										180,000,000
Fair value refinement period, maximum years		1
Net assets acquired		11,200,000,000
Business acquisition, purchase price allocation, loans and leases acquired		6,500,000,000
Business acquisition, purchase price allocation, investment securities acquired		2,600,000,000
Core deposit intangible				224,000,000
Business acquisition purchase price allocation deposits				9,200,000,000
Total liabilities acquired				10,100,000,000
Goodwill from Whitney acquisition at acquisition date		513,917,000								589,500,000
Goodwill reduced for deferred tax purchase accounting adjustments	22,300,000
Business combination, net income of acquirer included in consolidated statements		232,500,000
NetIncomeLoss	151,742,000	76,759,000	52,206,000						97,398,000	36,592,000	34,743,000
Merger related charges, total									45,800,000	86,800,000
Business acquisition, Merger related charges		86,800,000
Fair value of the acquired performing receivables				5,900,000,000
Gross contractual receivable				6,800,000,000
Contingent liabilities payments to employees, fair value				58,000,000
Contractual contingency assumed liabilities for systems conversion and replacement initiative, fair value	14,000,000
Payment against liability	$ 2,600,000	$ 1,100,000