Deposits (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Deposits [Line Items]
Total non-interest-bearing demand deposits	$ 6,672,555	$ 5,360,436
Total interest-bearing deposits	10,084,193	9,118,906
Total deposits	16,756,748	14,479,342
Private Accounts [Member]
Deposits [Line Items]
Savings and interest checking	2,912,937	2,505,143
Money market accounts	5,664,780	4,949,764
Time accounts of $100,000 or more	533,682	611,836
Time accounts under $100,000	522,887	571,447
Total private accounts	9,634,286	8,638,190
Commercial And Individual [Member]
Deposits [Line Items]
Total non-interest-bearing demand deposits	5,848,840	4,791,149
Correspondent Banks [Member]
Deposits [Line Items]
Total non-interest-bearing demand deposits	370,275	361,100
Public Funds [Member]
Deposits [Line Items]
Total non-interest-bearing demand deposits	453,440	208,187
Savings and interest checking	265,747	255,605
Money market accounts	44,590	84,093
Time accounts of $100,000 or more	136,422	137,506
Time accounts under $100,000	3,148	3,512
Total public funds	$ 449,907	$ 480,716