Accounting for Certain Loans Acquired in a Purchase - Accretable Yield or Income Expected to be Collected (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Beginning balance	$ 2,607	$ 4,627	$ 3,951	$ 5,612
Additions	941		1,608
Accretion	(686)	(1,012)	(5,082)	(4,623)
Reclassification from nonaccretable	449	698	3,501	3,567
Disposals			(667)	(243)
Ending balance	3,311	4,313	3,311	4,313
IAB
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Beginning balance
Additions	941		941
Accretion
Reclassification from nonaccretable
Disposals
Ending balance	941		941
Arlington Bank
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Beginning balance	667
Additions			667
Accretion	(38)		(38)
Reclassification from nonaccretable	26		26
Disposals
Ending balance	655		655
Ameriana
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Beginning balance	671	1,846	1,630	2,160
Additions
Accretion	(156)	(67)	(2,814)	(154)
Reclassification from nonaccretable	23	4	1,722	9
Disposals				(232)
Ending balance	538	1,783	538	1,783
C Financial
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Beginning balance	63	81	73	114
Additions
Accretion	(134)	(18)	(222)	(104)
Reclassification from nonaccretable	71	15	149	68
Disposals
Ending balance		78		78
Community
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Beginning balance	890	1,345	1,233	1,508
Additions
Accretion	(11)	(63)	(444)	(975)
Reclassification from nonaccretable		22	212	771
Disposals			(122)
Ending balance	879	1,304	879	1,304
CFS
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Beginning balance	81	904	736	1,188
Additions
Accretion	(166)	(665)	(1,053)	(2,810)
Reclassification from nonaccretable	170	585	947	2,457
Disposals			(545)	(11)
Ending balance	85	824	85	824
SCB
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward]
Beginning balance	235	451	279	642
Additions
Accretion	(181)	(199)	(511)	(580)
Reclassification from nonaccretable	159	72	445	262
Disposals
Ending balance	$ 213	$ 324	$ 213	$ 324