Credit Quality of Loans and Allowance for Loan Losses - Narrative (Details)	9 Months Ended
	Sep. 30, 2017 USD ($) industry_concentration	Dec. 31, 2016 USD ($)
Financing Receivable, Recorded Investment [Line Items]
Number of industry segment concentration above threshold limit | industry_concentration	1
Concentration Risk, Percentage	10.00%
Loans exposure in oil and gas industry	$ 197,800,000
Exposure in the oil and gas industry specified as percentage of total loans	16.00%
Loans with exposure in commercial real estate	$ 537,900,000
Loans on nonaccrual status	$ 51,289,000	$ 62,580,000
Nonaccrual status of loans specified as percentage of total CRE loans	3.80%
Loans and Leases Receivable, Impaired, Commitment to Lend	$ 0
Real estate – commercial
Financing Receivable, Recorded Investment [Line Items]
Percentage of CRE loans secured by owner-occupied commercial properties	56.00%
Total CRE loans on non-accrual	$ 20,500,000
Loans on nonaccrual status	$ 18,132,000	$ 28,688,000