LOANS AND ALLOWANCE - Aging of the Recorded Investment in Past Due Loans - (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Recorded investment in nonaccrual and loans past due over 90 days still on accrual and aging of recorded investment in past due
Non-accrual	$ 19,436	$ 15,808
Past due over 90 days and still accruing		2,135
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	3,028,686	2,651,673
Total Past Due	16,052	23,234
Loans Not Past Due	3,012,634	2,628,439
Accrued interest	8,060	7,342
30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	2,330	9,640
60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	2,597	2,229
Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	11,125	11,365
Cheviot Financial Corp.
Recorded investment in nonaccrual and loans past due over 90 days still on accrual and aging of recorded investment in past due
Non-accrual	7,290	3,564
Commercial
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	555,629	534,559
Commercial | Commercial and industrial
Recorded investment in nonaccrual and loans past due over 90 days still on accrual and aging of recorded investment in past due
Non-accrual	490	882
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	492,942	461,092
Total Past Due	230	176
Loans Not Past Due	492,712	460,916
Commercial | Commercial and industrial | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	56
Commercial | Commercial and industrial | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	174	176
Commercial | Agricultural
Recorded investment in nonaccrual and loans past due over 90 days still on accrual and aging of recorded investment in past due
Non-accrual	1,569	1,631
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	62,687	73,467
Total Past Due	1,578	1,821
Loans Not Past Due	61,109	71,646
Commercial | Agricultural | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	15	215
Commercial | Agricultural | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	15
Commercial | Agricultural | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	1,548	1,606
Commercial Real Estate
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	1,423,915	1,162,696
Commercial Real Estate | Farm
Recorded investment in nonaccrual and loans past due over 90 days still on accrual and aging of recorded investment in past due
Non-accrual	1,659	1,347
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	101,859	111,807
Total Past Due	1,567	1,324
Loans Not Past Due	100,292	110,483
Commercial Real Estate | Farm | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	6	81
Commercial Real Estate | Farm | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	22
Commercial Real Estate | Farm | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	1,539	1,243
Commercial Real Estate | Hotel
Recorded investment in nonaccrual and loans past due over 90 days still on accrual and aging of recorded investment in past due
Non-accrual	2,950	64
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	117,027	91,213
Total Past Due		63
Loans Not Past Due	117,027	91,150
Commercial Real Estate | Hotel | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due		63
Commercial Real Estate | Construction and development
Recorded investment in nonaccrual and loans past due over 90 days still on accrual and aging of recorded investment in past due
Non-accrual	1,416	122
Past due over 90 days and still accruing		2,135
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	123,521	102,598
Total Past Due	1,416	3,639
Loans Not Past Due	122,105	98,959
Commercial Real Estate | Construction and development | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due		1,416
Commercial Real Estate | Construction and development | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	1,416	2,223
Commercial Real Estate | Other
Recorded investment in nonaccrual and loans past due over 90 days still on accrual and aging of recorded investment in past due
Non-accrual	3,543	3,219
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	1,081,508	857,078
Total Past Due	3,121	3,170
Loans Not Past Due	1,078,387	853,908
Commercial Real Estate | Other | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	817	1,268
Commercial Real Estate | Other | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	224	90
Commercial Real Estate | Other | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	2,080	1,812
Residential
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	983,915	892,513
Residential | 1-4 family
Recorded investment in nonaccrual and loans past due over 90 days still on accrual and aging of recorded investment in past due
Non-accrual	5,854	7,163
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	684,187	608,366
Total Past Due	5,910	10,148
Loans Not Past Due	678,277	598,218
Residential | 1-4 family | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	911	4,884
Residential | 1-4 family | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	2,102	2,002
Residential | 1-4 family | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	2,897	3,262
Residential | Home equity
Recorded investment in nonaccrual and loans past due over 90 days still on accrual and aging of recorded investment in past due
Non-accrual	992	1,273
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	299,728	284,147
Total Past Due	1,154	1,881
Loans Not Past Due	298,574	282,266
Residential | Home equity | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	421	830
Residential | Home equity | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	214	137
Residential | Home equity | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	519	914
Consumer
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	65,227	61,905
Consumer | Direct
Recorded investment in nonaccrual and loans past due over 90 days still on accrual and aging of recorded investment in past due
Non-accrual	963	107
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	64,958	61,574
Total Past Due	1,076	1,002
Loans Not Past Due	63,882	60,572
Consumer | Direct | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	104	936
Consumer | Direct | 60-89 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	20
Consumer | Direct | Greater Than 90 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due	952	66
Consumer | Indirect
Aging of the recorded investment in past due loans
Total ending loan balance excluding accrued interest	269	331
Total Past Due		10
Loans Not Past Due	$ 269	321
Consumer | Indirect | 30-59 Days Past Due
Aging of the recorded investment in past due loans
Total Past Due		$ 10