Goodwill - Narrative (Details) - USD ($)	3 Months Ended		12 Months Ended
	Sep. 30, 2017	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Jul. 14, 2017	May 19, 2017	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill			$ 445,355,000	$ 244,000,000			$ 243,129,000
Measurement period adjustment			(469,000)	871,000
Goodwill impairment loss			$ 0	$ 0
IAB
Business Acquisition [Line Items]
Goodwill					$ 153,636,000
Arlington Bank
Business Acquisition [Line Items]
Goodwill						$ 47,719,000
Measurement period adjustment	$ 469,000
Merger with Ameriana Bancorp
Business Acquisition [Line Items]
Goodwill							$ 38,624,000
Measurement period adjustment		$ 871,000