Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
	Sep. 08, 2016	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Goodwill and Intangible Assets Gross Carrying Value [Abstract]
Goodwill not subject to amortization			$ 63,910	$ 61,551
Intangibles from branch acquisition			3,015	3,015
Core deposit intangibles			19,862	19,862
Customer list intangibles			3,731	3,731
Total Goodwill and Intangible Assets, Gross Carrying Value			90,518	88,159
Goodwill and Intangible Assets Accumulated Amortization [Abstract]
Goodwill not subject to amortization (effective 1/1/02), Accumulated Amortization			3,760	3,760
Total Goodwill and Intangible Assets, Accumulated Amortization			20,533	18,521
Total Amortization Expense [Abstract]
Amortization of intangible assets			2,153	1,909	$ 891
Estimated amortization expense [Abstract]
For year ended 12/31/18			1,954
For year ended 12/31/19			1,778
For year ended 12/31/20			1,576
For year ended 12/31/21			1,304
For year ended 12/31/22			1,195
First Clover Leaf [Member]
Estimated amortization expense [Abstract]
Goodwill, Acquired During Period	$ 19,143	$ 19,143
Intangibles from branch acquisitions
Goodwill and Intangible Assets Accumulated Amortization [Abstract]
Intangible Assets, Accumulated Amortization			3,015	3,015
Core deposit intangibles
Goodwill and Intangible Assets Accumulated Amortization [Abstract]
Intangible Assets, Accumulated Amortization			11,473	9,644
Total Amortization Expense [Abstract]
Amortization of intangible assets			1,829	1,628	876
Customer list intangibles
Goodwill and Intangible Assets Accumulated Amortization [Abstract]
Intangible Assets, Accumulated Amortization			2,285	2,102
Total Amortization Expense [Abstract]
Amortization of intangible assets			183	183	15
Mortgage Servicing Rights [Member]
Total Amortization Expense [Abstract]
Amortization of intangible assets			$ 141	$ 98	$ 0