FAIR VALUE - Fair Value of Assets and Liabilities Measured on a Nonrecurring Basis - (Details) - Non-recurring basis - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Assets:
Impaired servicing rights	$ 928		$ 928		$ 1,083
Total impaired loans	6,889		6,889		2,537
Recorded investment of impaired loans	10,464		10,464		4,008
Valuation allowance of impaired loans	3,575		3,575		1,471
Provision expenses of impaired loans	1,748	$ 228	2,629	$ 634
Gross outstanding balance of servicing rights	1,103		1,103		1,283
Valuation allowance of servicing rights			175		200
Change occurred in the valuation allowance	25	$ 125	25	$ 175
Commercial and industrial
Assets:
Total impaired loans	855		855		260
Recorded investment of impaired loans	2,197		2,197
Valuation allowance of impaired loans	1,342		1,342
Agricultural
Assets:
Total impaired loans	779		779		972
Recorded investment of impaired loans	1,484		1,484
Valuation allowance of impaired loans	705		705
Hotel
Assets:
Total impaired loans	2,715		2,715
Recorded investment of impaired loans	2,918		2,918
Valuation allowance of impaired loans	203		203
Farm
Assets:
Total impaired loans	794		794		745
Recorded investment of impaired loans	1,344		1,344
Valuation allowance of impaired loans	550		550
Other real estate
Assets:
Total impaired loans	1,746		1,746		560
Recorded investment of impaired loans	2,521		2,521
Valuation allowance of impaired loans	775		775
Significant Unobservable Inputs (Level 3)
Assets:
Impaired servicing rights	928		928		1,083
Total impaired loans	6,889		6,889		2,537
Significant Unobservable Inputs (Level 3) | Commercial and industrial
Assets:
Total impaired loans	855		855		260
Significant Unobservable Inputs (Level 3) | Agricultural
Assets:
Total impaired loans	779		779		972
Significant Unobservable Inputs (Level 3) | Hotel
Assets:
Total impaired loans	2,715		2,715
Significant Unobservable Inputs (Level 3) | Farm
Assets:
Total impaired loans	794		794		745
Significant Unobservable Inputs (Level 3) | Other real estate
Assets:
Total impaired loans	$ 1,746		$ 1,746		$ 560