Loans Receivable and Allowance for Loan Losses (Summary of Loans Receivable) (Details) (USD $)	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Qualifying loans pledged as FHLB collateral	$ 512,800,000
Bank loans receivable, Gross	1,633,866,000		1,528,797,000
Bank loans receivable, Allowance for loan losses	28,038,000	27,472,000	25,282,000	26,158,000	23,759,000	21,620,000
Bank loans receivable, Net	1,605,828,000		1,503,515,000
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	415,740,000		376,988,000
Bank loans receivable, Allowance for loan losses	10,549,000	10,408,000	9,959,000	10,575,000	8,251,000	8,400,000
Commercial tax-exempt [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	82,455,000		92,202,000
Bank loans receivable, Allowance for loan losses	74,000	75,000	83,000	74,000	72,000	79,000
Owner occupied real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	288,702,000		268,372,000
Bank loans receivable, Allowance for loan losses	2,207,000	2,208,000	2,129,000	2,117,000	1,794,000	729,000
Commercial construction and land development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	105,596,000		100,399,000
Bank loans receivable, Allowance for loan losses	7,810,000	7,967,000	7,222,000	8,917,000	8,940,000	7,840,000
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	433,628,000		394,404,000
Bank loans receivable, Allowance for loan losses	5,059,000	5,038,000	3,983,000	3,139,000	3,347,000	3,241,000
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	90,590,000		83,899,000
Bank loans receivable, Allowance for loan losses	863,000	338,000	324,000	438,000	426,000	435,000
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	217,155,000		212,533,000
Bank loans receivable, Allowance for loan losses	$ 1,258,000	$ 787,000	$ 793,000	$ 797,000	$ 783,000	$ 831,000