Acquisitions (Details) $ / shares in Units, $ in Thousands		9 Months Ended	12 Months Ended
	Jan. 08, 2015 USD ($) item $ / shares	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition
Goodwill		$ 25,510	$ 20,686
Herget Financial and Herget Bank
Business Acquisition
Percentage of outstanding common stock to be acquired	100.00%
Aggregate cash consideration	$ 34,100
Per share cash consideration entitled (in dollars per share) | $ / shares	$ 588.00
Business acquisition expenses		$ 1,000	$ 400
Maximum period of measurement adjustments from the closing date of acquisition	1 year
Cash and due from banks	$ 46,214
Securities	111,760
Loans held for sale	1,933
Loans	105,207
Premises and equipment	2,034
Goodwill	4,824
Other intangible assets	3,937
Other assets	2,931
Deposits	241,901
Other liabilities	2,839
Fair value of performed loans	103,700
Fair value of credit-impaired loans	$ 1,500
Amortization period of other intangible assets	P10Y
Herget Bank
Business Acquisition
Number of branches | item	3