Regulatory Matters (Narrative) (Detail) (USD $)	3 Months Ended			3 Months Ended	9 Months Ended
	Sep. 30, 2012 Year	Dec. 31, 2011	Sep. 30, 2011	Sep. 30, 2012 Floating Rate Subordinated Notes [Member]	Sep. 30, 2012 Floating Rate Subordinated Notes [Member]
Regulatory Assets [Line Items]
Trust preferred securities	$ 120,000,000
Corporation's aggregate subordinated notes	123,712,000	123,712,000	123,712,000	100,000,000	100,000,000
Percentage of decreases in permissible portion				20.00%
Permissible portion					80,000,000
Maximum dividends available without prior regulatory approval	$ 281,100,000
Removal period of trust preferred securities from Tier 1 capital years	3