Loans Receivable and Allowance for Loan Losses (Credit Quality Indicators for Commercial Loans, by Loan Type) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013 loan	Dec. 31, 2012 loan
Financing Receivable, Recorded Investment [Line Items]
Number of loans classified as doubtful	0	0
Credit exposure for commercial loans	$ 1,393,557	$ 1,232,365
Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	435,508	376,988
Commercial tax-exempt [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	82,507	92,202
Owner occupied real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	300,555	268,372
Commercial construction and land development [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	124,376	100,399
Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	450,611	394,404
Pass Rated Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	1,305,991	1,141,535
Pass Rated Loans [Member] | Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	393,313	335,463
Pass Rated Loans [Member] | Commercial tax-exempt [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	82,507	92,202
Pass Rated Loans [Member] | Owner occupied real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	284,355	253,338
Pass Rated Loans [Member] | Commercial construction and land development [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	108,560	81,219
Pass Rated Loans [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	437,256	379,313
Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	14,044	15,900
Special Mention [Member] | Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	9,454	6,120
Special Mention [Member] | Commercial tax-exempt [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	0	0
Special Mention [Member] | Owner occupied real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	3,983	4,160
Special Mention [Member] | Commercial construction and land development [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	0	5,046
Special Mention [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	607	574
Substandard Accrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	40,004	48,563
Substandard Accrual [Member] | Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	22,774	24,116
Substandard Accrual [Member] | Commercial tax-exempt [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	0	0
Substandard Accrual [Member] | Owner occupied real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	7,293	7,755
Substandard Accrual [Member] | Commercial construction and land development [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	4,093	7,834
Substandard Accrual [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	5,844	8,858
Substandard Nonaccrual [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	33,518	26,367
Substandard Nonaccrual [Member] | Commercial and industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	9,967	11,289
Substandard Nonaccrual [Member] | Commercial tax-exempt [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	0	0
Substandard Nonaccrual [Member] | Owner occupied real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	4,924	3,119
Substandard Nonaccrual [Member] | Commercial construction and land development [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	11,723	6,300
Substandard Nonaccrual [Member] | Commercial real estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Credit exposure for commercial loans	$ 6,904	$ 5,659