Accounting for Certain Loans Acquired in a Purchase - Carrying Amount of Loans Included in Balance Sheet (Details) $ in Thousands	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($) loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	$ 1,443,246	$ 698,097
Remaining fair value discount	(47,878)	(32,680)
Carrying amount	1,395,368	665,417
Allowance	863	380
Loans acquired and accounted for under ASC 310-30, carrying amount	1,394,505	665,037
Loans Acquired with Deteriorated Credit Quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	42,100	60,500
Loans acquired and accounted for under ASC 310-30, carrying amount	26,800	43,200
Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	128,940	37,236
Agricultural production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	40,817	2,710
Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	61,106	29,298
Real estate loans - Commercial and farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	675,892	303,362
Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	396,388	257,640
Real estate loans - Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	117,262	64,819
Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	5,577	1,142
Lease financing receivables, net of unearned income
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	2,405
Other commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	14,859	1,890
Transferred to Other Real Estate Owned | Loans Acquired with Deteriorated Credit Quality
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance		12,100
Loans acquired and accounted for under ASC 310-30, carrying amount		$ 7,600
Loans transferred to Other Real Estate Owned, number | loan		1
IAB
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	715,563
Remaining fair value discount	(22,501)
Carrying amount	693,062
Allowance	362
Loans acquired and accounted for under ASC 310-30, carrying amount	692,700
IAB | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	107,827
IAB | Agricultural production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	39,558
IAB | Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	32,866
IAB | Real estate loans - Commercial and farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	370,664
IAB | Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	106,466
IAB | Real estate loans - Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	38,581
IAB | Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	4,236
IAB | Lease financing receivables, net of unearned income
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	2,405
IAB | Other commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	12,960
Arlington Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	203,887
Remaining fair value discount	(5,901)
Carrying amount	197,986
Loans acquired and accounted for under ASC 310-30, carrying amount	197,986
Arlington Bank | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	4,131
Arlington Bank | Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	16,025
Arlington Bank | Real estate loans - Commercial and farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	84,212
Arlington Bank | Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	71,752
Arlington Bank | Real estate loans - Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	26,918
Arlington Bank | Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	755
Arlington Bank | Other commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	94
Ameriana
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	198,390	$ 250,824
Remaining fair value discount	(7,065)	(10,771)
Carrying amount	191,325	240,053
Allowance	411	265
Loans acquired and accounted for under ASC 310-30, carrying amount	190,914	239,788
Ameriana | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	4,823	8,003
Ameriana | Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	9,269	22,017
Ameriana | Real estate loans - Commercial and farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	83,030	103,075
Ameriana | Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	89,773	103,414
Ameriana | Real estate loans - Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	9,333	11,728
Ameriana | Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	417	762
Ameriana | Other commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	1,745	1,825
C Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	60,579	77,100
Remaining fair value discount	(1,383)	(1,906)
Carrying amount	59,196	75,194
Loans acquired and accounted for under ASC 310-30, carrying amount	59,196	75,194
C Financial | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	70	85
C Financial | Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	1,122	2,835
C Financial | Real estate loans - Commercial and farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	18,149	22,130
C Financial | Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	35,027	44,101
C Financial | Real estate loans - Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	6,211	7,947
C Financial | Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance		2
Community
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	43,453	60,108
Remaining fair value discount	(2,545)	(4,101)
Carrying amount	40,908	56,007
Allowance	52	23
Loans acquired and accounted for under ASC 310-30, carrying amount	40,856	55,984
Community | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	409	2,269
Community | Agricultural production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	93	1,030
Community | Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	1,721	4,026
Community | Real estate loans - Commercial and farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	29,681	36,947
Community | Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	6,845	9,363
Community | Real estate loans - Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	4,615	6,326
Community | Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	89	147
CFS
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	197,692	279,479
Remaining fair value discount	(6,185)	(12,634)
Carrying amount	191,507	266,845
Allowance	38	92
Loans acquired and accounted for under ASC 310-30, carrying amount	191,469	266,753
CFS | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	9,509	23,327
CFS | Agricultural production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	50	50
CFS | Real estate loans - Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	103	420
CFS | Real estate loans - Commercial and farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	83,186	131,895
CFS | Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	83,421	96,627
CFS | Real estate loans - Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	21,306	26,894
CFS | Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	57	201
CFS | Other commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	60	65
SCB
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	23,682	30,586
Remaining fair value discount	(2,298)	(3,268)
Carrying amount	21,384	27,318
Loans acquired and accounted for under ASC 310-30, carrying amount	21,384	27,318
SCB | Commercial and industrial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	2,171	3,552
SCB | Agricultural production financing and other loans to farmers
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	1,116	1,630
SCB | Real estate loans - Commercial and farmland
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	6,970	9,315
SCB | Real estate loans - Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	3,104	4,135
SCB | Real estate loans - Home Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	10,298	11,924
SCB | Individuals' loans for household and other personal expenditures
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans acquired and accounted for under ASC 310-30, outstanding balance	$ 23	$ 30