Regulatory Matters (Narrative) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012 Y	Dec. 31, 2011
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Trust preferred securities	$ 120,000,000	$ 120,000,000
Corporation's aggregate subordinated notes	123,712,000	123,712,000
Maximum dividends available without prior regulatory approval	306,500,000
Removal period of trust preferred securities from Tier 1 capital years	4
Floating Rate Subordinated Notes [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Corporation's aggregate subordinated notes	100,000,000
Percentage of decreases in permissible portion	20.00%
Permissible portion of subordinated note included in capital	$ 80,000,000	$ 100,000,000