Deposits (Deposits) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010
Total non-interest-bearing demand deposits, balance	$ 5,818,692	$ 5,360,436	$ 5,062,023
Total non-interest-bearing demand deposits, percent	38.50%	37.00%	36.30%
Total interest-bearing deposits, balance	9,285,439	9,118,906	8,890,137
Total interest-bearing deposits, percent	61.50%	63.00%	63.70%
Total deposits, balance	15,104,131	14,479,342	13,952,160
Total deposits, percent	100.00%	100.00%	100.00%
Private Accounts [Member]
Savings and interest checking, balance	2,449,434	2,505,143	2,241,164
Savings and interest checking, percent	16.20%	17.30%	16.10%
Money market accounts, balance	5,331,994	4,949,764	4,948,612
Money market accounts, percent	35.30%	34.20%	35.50%
Time accounts of $100,000 or more, balance	582,183	611,836	662,029
Time accounts of $100,000 or more, percent	3.90%	4.20%	4.70%
Time accounts under $100,000, balance	539,715	571,447	620,159
Time accounts under $100,000, percent	3.60%	4.00%	4.40%
Total private accounts, balance	8,903,326	8,638,190	8,471,964
Total private account, percent	59.00%	59.70%	60.70%
Commercial and Individual [Member]
Total non-interest-bearing demand deposits, balance	5,220,598	4,791,149	4,608,543
Total non-interest-bearing demand deposits, percent	34.60%	33.10%	33.00%
Correspondent Banks [Member]
Total non-interest-bearing demand deposits, balance	274,465	361,100	290,817
Total non-interest-bearing demand deposits, percent	1.80%	2.50%	2.10%
Public Funds [Member]
Total non-interest-bearing demand deposits, balance	323,629	208,187	162,663
Total non-interest-bearing demand deposits, percent	2.10%	1.40%	1.20%
Savings and interest checking, balance	194,778	255,605	196,591
Savings and interest checking, percent	1.30%	1.80%	1.40%
Money market accounts, balance	49,561	84,093	79,081
Money market accounts, percent	0.30%	0.60%	0.60%
Time accounts of $100,000 or more, balance	133,508	137,506	138,273
Time accounts of $100,000 or more, percent	0.90%	0.90%	1.00%
Time accounts under $100,000, balance	4,266	3,512	4,228
Time accounts under $100,000, percent
Total public funds, balance	$ 382,113	$ 480,716	$ 418,173
Total public funds, percent	2.50%	3.30%	3.00%