Other Intangibles - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2016	Sep. 30, 2017	Dec. 31, 2016	Jul. 14, 2017	May 19, 2017	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Measurement period adjustment			$ 2,142
Core deposits | Minimum
Finite-Lived Intangible Assets [Line Items]
Useful life of core deposit intangibles and other intangibles		2 years
Core deposits | Maximum
Finite-Lived Intangible Assets [Line Items]
Useful life of core deposit intangibles and other intangibles		10 years
IAB
Finite-Lived Intangible Assets [Line Items]
Core deposit intangible				$ 17,403
IAB | Core deposits
Finite-Lived Intangible Assets [Line Items]
Core deposit intangible				13,638
IAB | Noncompete agreements
Finite-Lived Intangible Assets [Line Items]
Core deposit intangible				$ 3,765
Arlington Bank
Finite-Lived Intangible Assets [Line Items]
Core deposit intangible					$ 4,526
Arlington Bank | Core deposits
Finite-Lived Intangible Assets [Line Items]
Core deposit intangible					$ 4,526
Ameriana
Finite-Lived Intangible Assets [Line Items]
Measurement period adjustment	$ 2,142
Ameriana | Core deposits
Finite-Lived Intangible Assets [Line Items]
Core deposit intangible						$ 5,342