Nature of Operations and Summary of Significant Accounting Policies - Other (Details)	1 Months Ended	12 Months Ended
	Aug. 31, 2017 USD ($)	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Nature of Operations and Principles of Consolidation
Number of locations of operation | item		4
Goodwill		$ 3,902,000	$ 523,000	$ 523,000	$ 523,000
Cash and Cash Equivalents
Cash accounts in excess of federally insured limits		349,400,000	437,500,000
Cash accounts in excess of federally insured limits with Federal Reserve Bank		327,400,000	426,100,000
Cash accounts in excess of federally insured limits with Federal Home Loan Bank of Indianapolis		3,500,000	2,800,000
Securities
Unrealized gains included in securities		$ 643,000	$ 1,700,000	$ 1,700,000
Loans Held for Sale under Mortgage Banking Activities
Maximum participation interest to be purchased in individual loans (as a percent)		100.00%
RICHMAC
Nature of Operations and Principles of Consolidation
Purchase price paid shares	$ 8,100,000
Goodwill	3,400,000
Intangible assets	$ 1,600,000