Summary Of Significant Accounting Policies (Narrative) (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2012 Region	Dec. 31, 2011	Dec. 31, 2010
Summary Of Significant Accounting Policies [Line Items]
Number of Metropolitan Statistical Areas		5
Loan fees amortized and included in interest income		$ 10,765,000	$ 6,264,000	$ 4,690,000
Minimum days, related to accrual of interest on discontinued commercial and consumer loans		90 days
Maximum days, related to accrual of interest on discontinued commercial and consumer loans		120 days
Sustained period of repayment performance in restructured loans		6 months
Real estate acquired in foreclosure or other settlement of loans		49,484,000	51,760,000
Advertising expense		4,270,000	4,172,000	4,226,000
Amortization expense on intangible assets		2,852,000	2,429,000	1,884,000
Total goodwill		375,583,000	375,626,000
Stock based compensation expense		$ 1,908,000	$ 1,133,000	$ 1,050,000
Equivalents from stock options		32,399	33,931	77,218
Restricted shares, granted	52,700
Restricted shares, vesting period	Four-year
Minimum [Member] | Core Deposit Intangible Assets [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortized intangible assets, useful life		1 year
Maximum [Member] | Core Deposit Intangible Assets [Member]
Summary Of Significant Accounting Policies [Line Items]
Amortized intangible assets, useful life		7 years
Furniture Fixtures And Equipment [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Bank premises and equipment, useful life		3 years
Furniture Fixtures And Equipment [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Bank premises and equipment, useful life		15 years
Buildings And Improvements [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Bank premises and equipment, useful life		5 years
Buildings And Improvements [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Bank premises and equipment, useful life		40 years