Loans Receivable - Schedule of Loans Receivable (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Loans Receivable [Line Items]
Total loans receivable	$ 8,594,975	$ 8,498,580
Residential Mortgage Loans [Member]
Loans Receivable [Line Items]
Total loans receivable	478,617	477,204
Residential Mortgage Loans [Member] | Residential 1-4 Family [Member]
Loans Receivable [Line Items]
Total loans receivable	473,503	471,183
Residential Mortgage Loans [Member] | Construction/ Owner Occupied [Member]
Loans Receivable [Line Items]
Total loans receivable	5,114	6,021
Commercial Loans [Member]
Loans Receivable [Line Items]
Total loans receivable	6,209,336	6,169,261
Commercial Loans [Member] | Real Estate [Member]
Loans Receivable [Line Items]
Total loans receivable	3,587,692	3,631,543
Commercial Loans [Member] | Business [Member]
Loans Receivable [Line Items]
Total loans receivable	2,621,644	2,537,718
Consumer And Other Loans [Member]
Loans Receivable [Line Items]
Total loans receivable	1,907,022	1,852,115
Consumer And Other Loans [Member] | Indirect Automobile [Member]
Loans Receivable [Line Items]
Total loans receivable	342,117	327,985
Consumer And Other Loans [Member] | Home Equity [Member]
Loans Receivable [Line Items]
Total loans receivable	1,261,171	1,251,125
Consumer And Other Loans [Member] | Other [Member]
Loans Receivable [Line Items]
Total loans receivable	$ 303,734	$ 273,005