Loans Receivable and Allowance for Loan Losses (Summary of Loans Receivable) (Details) (USD $)	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Qualifying loans pledged as FHLB collateral	$ 599,200,000
Bank loans receivable, Gross	1,702,676,000		1,528,797,000
Bank loans receivable, Allowance for loan losses	27,425,000	28,038,000	25,282,000	25,596,000	26,158,000	21,620,000
Bank loans receivable, Net	1,675,251,000		1,503,515,000
Commercial and industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	435,508,000		376,988,000
Bank loans receivable, Allowance for loan losses	9,263,000	10,549,000	9,959,000	10,501,000	10,575,000	8,400,000
Commercial tax-exempt [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	82,507,000		92,202,000
Bank loans receivable, Allowance for loan losses	75,000	74,000	83,000	80,000	74,000	79,000
Owner occupied real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	300,555,000		268,372,000
Bank loans receivable, Allowance for loan losses	2,177,000	2,207,000	2,129,000	2,411,000	2,117,000	729,000
Commercial construction and land development [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	124,376,000		100,399,000
Bank loans receivable, Allowance for loan losses	7,489,000	7,810,000	7,222,000	7,594,000	8,917,000	7,840,000
Commercial real estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	450,611,000		394,404,000
Bank loans receivable, Allowance for loan losses	5,751,000	5,059,000	3,983,000	3,223,000	3,139,000	3,241,000
Residential [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	94,227,000		83,899,000
Bank loans receivable, Allowance for loan losses	879,000	863,000	324,000	344,000	438,000	435,000
Consumer [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Bank loans receivable, Gross	214,892,000		212,533,000
Bank loans receivable, Allowance for loan losses	$ 1,316,000	$ 1,258,000	$ 793,000	$ 789,000	$ 797,000	$ 831,000