Business Segments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Segment Reporting [Abstract]
Federal and State Effective Tax Rate Used for Segment Reporting	37.00%
Business segment financial information
Net Interest Income	$ 88,560	$ 97,948
Provision for Credit Losses	0	351
Net Interest Income After Provision for Credit Losses	88,560	97,597
Noninterest Income	47,778	48,082
Noninterest Expense	(84,387)	(85,207)
Income Before Provision for Income Taxes	51,951	60,472
Provision for Income Taxes	(15,971)	(16,662)
Net Income	35,980	43,810
Total Assets	13,525,667	13,759,409	13,728,372
Retail Banking
Business segment financial information
Number of branch locations through which products and services are delivered to customers	65
Number of ATM's through which products and services are delivered to customers	489
Net Interest Income	35,909	40,185
Provision for Credit Losses	2,178	4,030
Net Interest Income After Provision for Credit Losses	33,731	36,155
Noninterest Income	20,484	19,540
Noninterest Expense	(44,454)	(44,612)
Income Before Provision for Income Taxes	9,761	11,083
Provision for Income Taxes	(3,612)	(4,101)
Net Income	6,149	6,982
Total Assets	3,282,022	3,257,404
Commercial Banking
Business segment financial information
Number of branches in which international banking and operations is included	10
Net Interest Income	29,872	31,442
Provision for Credit Losses	(171)	(668)
Net Interest Income After Provision for Credit Losses	30,043	32,110
Noninterest Income	9,400	11,577
Noninterest Expense	(22,884)	(23,522)
Income Before Provision for Income Taxes	16,559	20,165
Provision for Income Taxes	(5,672)	(3,021)
Net Income	10,887	17,144
Total Assets	2,482,837	2,294,017
Investment Services
Business segment financial information
Net Interest Income	2,771	3,333
Provision for Credit Losses	(21)	(12)
Net Interest Income After Provision for Credit Losses	2,792	3,345
Noninterest Income	14,810	13,670
Noninterest Expense	(14,135)	(14,762)
Income Before Provision for Income Taxes	3,467	2,253
Provision for Income Taxes	(1,283)	(833)
Net Income	2,184	1,420
Total Assets	188,662	192,554
Treasury and Other
Business segment financial information
Net Interest Income	20,008	22,988
Provision for Credit Losses	(1,986)	(2,999)
Net Interest Income After Provision for Credit Losses	21,994	25,987
Noninterest Income	3,084	3,295
Noninterest Expense	(2,914)	(2,311)
Income Before Provision for Income Taxes	22,164	26,971
Provision for Income Taxes	(5,404)	(8,707)
Net Income	16,760	18,264
Total Assets	$ 7,572,146	$ 8,015,434