Loans and Allowance - Allowance for Credit Losses and Loan Portfolio by Loan Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance balances - Individually evaluated for impairment	$ 1,645		$ 2,119
Allowance balances - Collectively evaluated for impairment	60,905		61,195
Total Allowance for Loan Losses	62,861	$ 62,550	63,964	$ 65,596	$ 68,367	$ 67,870
Loan balances - Individually evaluated for impairment	32,525		44,093
Loan balances - Collectively evaluated for impairment	4,227,200		3,807,707
Loans	4,321,715		3,924,865
Loans Acquired with Deteriorated Credit Quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance for Loan Losses	311		650
Loans	61,990		73,065
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance balances - Individually evaluated for impairment	1,268		1,455
Allowance balances - Collectively evaluated for impairment	32,668		27,369
Total Allowance for Loan Losses	33,936	31,479	28,824	27,542	28,614	27,176
Loan balances - Individually evaluated for impairment	8,192		16,108
Loan balances - Collectively evaluated for impairment	1,243,032		1,011,122
Loans	$ 1,258,539		$ 1,036,633
Commercial | Loans Acquired with Deteriorated Credit Quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance for Loan Losses
Loans	$ 7,315		$ 9,403
Commercial Real Estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance balances - Individually evaluated for impairment	304		470
Allowance balances - Collectively evaluated for impairment	13,480		18,207
Total Allowance for Loan Losses	13,986	15,828	19,327	21,618	22,582	23,102
Loan balances - Individually evaluated for impairment	19,466		23,963
Loan balances - Collectively evaluated for impairment	1,924,902		1,796,797
Loans	1,993,953		1,879,882
Commercial Real Estate | Loans Acquired with Deteriorated Credit Quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance for Loan Losses	202		650
Loans	$ 49,585		59,122
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance balances - Individually evaluated for impairment
Allowance balances - Collectively evaluated for impairment	$ 2,723		2,658
Total Allowance for Loan Losses	2,723	2,927	2,658	2,228	2,243	2,515
Loan balances - Collectively evaluated for impairment	71,893		73,400
Loans	$ 71,893		$ 73,400
Consumer | Loans Acquired with Deteriorated Credit Quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance for Loan Losses
Loans
Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance balances - Individually evaluated for impairment	$ 73		$ 194
Allowance balances - Collectively evaluated for impairment	12,031		12,958
Total Allowance for Loan Losses	12,213	12,311	13,152	14,207	$ 14,928	$ 15,077
Loan balances - Individually evaluated for impairment	4,867		4,022
Loan balances - Collectively evaluated for impairment	986,759		925,282
Loans	996,716		$ 933,844
Residential | Loans Acquired with Deteriorated Credit Quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance for Loan Losses	109
Loans	5,090		$ 4,540
Finance Leases
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance balances - Collectively evaluated for impairment	3		3
Total Allowance for Loan Losses	3	$ 5	3	$ 1
Loan balances - Collectively evaluated for impairment	614		1,106
Loans	$ 614		$ 1,106
Finance Leases | Loans Acquired with Deteriorated Credit Quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Total Allowance for Loan Losses
Loans