Loans Receivable and Allowance for Loan Losses (Summary of Loans Receivable) (Details) (USD $)	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010
Accounts, Notes, Loans and Financing Receivable [Line Items]
Qualifying loans pledged as FHLB collateral	$ 259,700,000
Bank loans receivable, Gross	1,492,755,000		1,436,668,000
Bank loans receivable, Allowance for loan losses	26,158,000	23,759,000	21,620,000	21,723,000	21,850,000	21,618,000
Bank loans receivable, Net	1,466,597,000		1,415,048,000
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	356,743,000		321,988,000
Bank loans receivable, Allowance for loan losses	10,575,000	8,251,000	8,400,000	8,951,000	8,861,000	9,679,000
Commercial tax-exempt [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	84,616,000		81,532,000
Bank loans receivable, Allowance for loan losses	74,000	72,000	79,000	81,000	83,000	86,000
Owner occupied real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	274,504,000		279,372,000
Bank loans receivable, Allowance for loan losses	2,117,000	1,794,000	729,000	994,000	942,000	910,000
Commercial construction and land development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	108,019,000		103,153,000
Bank loans receivable, Allowance for loan losses	8,917,000	8,940,000	7,840,000	5,391,000	6,016,000	5,420,000
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	377,248,000		364,405,000
Bank loans receivable, Allowance for loan losses	3,139,000	3,347,000	3,241,000	5,035,000	4,583,000	4,002,000
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	84,380,000		83,940,000
Bank loans receivable, Allowance for loan losses	438,000	426,000	435,000	438,000	461,000	442,000
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	207,245,000		202,278,000
Bank loans receivable, Allowance for loan losses	$ 797,000	$ 783,000	$ 831,000	$ 773,000	$ 761,000	$ 702,000