Acquisitions (Details)		3 Months Ended	6 Months Ended	12 Months Ended
	Jan. 08, 2015 USD ($) item	Jun. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition
Goodwill		$ 25,510,000	$ 25,510,000	$ 20,686,000
Herget Financial and Herget Bank
Business Acquisition
Percentage of outstanding common stock to be acquired	100.00%
Aggregate cash consideration	$ 34,100,000
Per share cash consideration entitled (in dollars per share)	$ 588.00
Business acquisition expenses		$ 100,000	$ 1,000,000	$ 400,000
Maximum period of measurement adjustments from the closing date of acquisition	1 year
Cash and due from banks	$ 46,214,000
Securities	111,760,000
Loans held for sale	1,933,000
Loans	105,207,000
Premises and equipment	2,034,000
Goodwill	4,824,000
Other intangible assets	3,937,000
Other assets	2,931,000
Deposits	241,901,000
Other liabilities	2,839,000
Fair value of performed loans	103,700,000
Fair value of credit-impaired loans	$ 1,500,000
Amortization period of other intangible assets	P10Y
Herget Bank
Business Acquisition
Number of branches | item	3