Loans Receivable and Allowance for Loan Losses (Summary of Loans Receivable) (Details) (USD $)	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Qualifying loans pledged as FHLB collateral	$ 98,600,000
Bank loans receivable, Gross	1,504,990,000		1,436,668,000
Bank loans receivable, Allowance for loan losses	25,596,000	26,158,000	21,620,000	23,307,000	21,723,000	21,618,000
Bank loans receivable, Net	1,479,394,000		1,415,048,000
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	347,099,000		321,988,000
Bank loans receivable, Allowance for loan losses	10,501,000	10,575,000	8,400,000	9,904,000	8,951,000	9,679,000
Commercial tax-exempt [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	88,934,000		81,532,000
Bank loans receivable, Allowance for loan losses	80,000	74,000	79,000	78,000	81,000	86,000
Owner occupied real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	274,235,000		279,372,000
Bank loans receivable, Allowance for loan losses	2,411,000	2,117,000	729,000	685,000	994,000	910,000
Commercial construction and land development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	107,311,000		103,153,000
Bank loans receivable, Allowance for loan losses	7,594,000	8,917,000	7,840,000	6,640,000	5,391,000	5,420,000
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	393,182,000		364,405,000
Bank loans receivable, Allowance for loan losses	3,223,000	3,139,000	3,241,000	4,719,000	5,035,000	4,002,000
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	82,989,000		83,940,000
Bank loans receivable, Allowance for loan losses	344,000	438,000	435,000	408,000	438,000	442,000
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	211,240,000		202,278,000
Bank loans receivable, Allowance for loan losses	$ 789,000	$ 797,000	$ 831,000	$ 823,000	$ 773,000	$ 702,000