Subsequent Events - Narrative (Details) $ / shares in Units, $ in Thousands	Apr. 24, 2020 USD ($) branch office state atm $ / shares shares	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Subsequent Event [Line Items]
Total assets		$ 10,681,196	$ 10,493,908
Subsequent Event
Subsequent Event [Line Items]
Total assets	$ 12,800,000
Number of branch locations | branch	214
Number of ATMs | atm	273
Number of states with branch and ATM locations | state	4
Mutual First Financial, Inc. | Subsequent Event
Subsequent Event [Line Items]
Total consideration	$ 213,400
Entity shares issued per acquiree share (in shares) | shares	2.4
Number of shares issued for purchase (in shares) | shares	20,659,087
Value of stock issued for purchase	$ 213,400
Value of stock issued (in dollars per share) | $ / shares	$ 10.33
Cash paid in lieu of fractional shares, per whole share (in dollars per share) | $ / shares	$ 10.71
Indiana | Subsequent Event
Subsequent Event [Line Items]
Number of offices acquired | office	36