Loans (Credit Quality Indicators) (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011	Jun. 30, 2011
Loans [Line Items]
Special Mention	$ 108,052		$ 204,965
Percentage of Portfolio Loan Type	1.10%		2.30%
Potential Problem Loans	164,077		177,095
Percentage of Portfolio Loan Type	1.70%		2.00%
Non-Performing Loans	209,339		259,852
Percentage of Portfolio Loan Type	2.20%		2.90%
Total loans	9,436,235		9,008,561	8,672,642
Commercial Loan [Member]
Loans [Line Items]
Special Mention	55,978		54,326
Percentage of Portfolio Loan Type	0.90%		1.00%
Potential Problem Loans	62,922		79,328
Percentage of Portfolio Loan Type	1.10%		1.50%
Non-Performing Loans	59,841		65,958
Percentage of Portfolio Loan Type	1.00%		1.20%
Total loans	5,908,611		5,323,774
Commercial Real Estate [Member]
Loans [Line Items]
Special Mention	42,978		132,915
Percentage of Portfolio Loan Type	1.60%		4.90%
Potential Problem Loans	74,864		62,193
Percentage of Portfolio Loan Type	2.90%		2.30%
Non-Performing Loans	119,444		133,257
Percentage of Portfolio Loan Type	4.60%		5.00%
Total loans	2,623,742		2,686,446
Construction Loans [Member]
Loans [Line Items]
Special Mention	5,844		7,272
Percentage of Portfolio Loan Type	3.40%		2.50%
Potential Problem Loans			9,283
Percentage of Portfolio Loan Type			3.20%
Non-Performing Loans	555		21,879
Percentage of Portfolio Loan Type	0.30%		7.60%
Total loans	171,014		287,002
Residential Real Estate [Member]
Loans [Line Items]
Special Mention	2,729		9,344
Percentage of Portfolio Loan Type	0.80%		3.10%
Potential Problem Loans	19,612		17,931
Percentage of Portfolio Loan Type	5.90%		6.00%
Non-Performing Loans	11,028		14,589
Percentage of Portfolio Loan Type	3.30%		4.90%
Total loans	330,254		297,229
Home Equity Line of Credit [Member]
Loans [Line Items]
Special Mention	516		758
Percentage of Portfolio Loan Type	0.30%		0.40%
Potential Problem Loans	5,856		6,384
Percentage of Portfolio Loan Type	3.40%		3.50%
Non-Performing Loans	12,063		11,603
Percentage of Portfolio Loan Type	6.90%		6.40%
Total loans	174,131		181,158
Consumer Loan [Member]
Loans [Line Items]
Special Mention	7		350
Percentage of Portfolio Loan Type		[1]	0.20%
Potential Problem Loans	823		1,976
Percentage of Portfolio Loan Type	0.40%		0.80%
Non-Performing Loans	6,408		12,566
Percentage of Portfolio Loan Type	2.80%		5.40%
Total loans	$ 228,483		$ 232,952

[1] Less than 0.1%