Investment Securities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($) Security Segment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Investment [Line Items]
Proceeds from sales of investment securities held-to-maturity		$ 855,000
Net securities gains	$ 5,848,000	5,718,000	$ 9,830,000
Securities pledged to secure public and other funds, carrying value	1,400,000,000	1,400,000,000
Trading securities that consist of mutual funds	$ 4,982,000	3,941,000
Number of segments | Segment	2
Other-than-temporary-impairment losses on securities	$ 0	0	100,000
Number of securities in security portfolio | Security	1,715
Number of securities in unrealized loss position | Security	507
Unrealized losses	$ 73,936,000	31,608,000
Other-than-temporary-impairment losses			$ 100,000
Municipal Bonds [Member]
Investment [Line Items]
Proceeds from sales of investment securities held-to-maturity		800,000
Net securities gains		52,000
Eastern Indiana [Member]
Investment [Line Items]
Investment securities issued by states and political subdivisions, market value	$ 369,400,000
State and political subdivision investment, equity percentage	20.40%
Percentage of municipal bonds rated A or better	97.00%
Percentage of non rated local interest bonds	3.00%
Texas [Member]
Investment [Line Items]
Investment securities issued by states and political subdivisions, market value	$ 198,200,000
State and political subdivision investment, equity percentage	10.90%
Former Directors and Executives [Member]
Investment [Line Items]
Trading securities that consist of mutual funds	$ 5,000,000	3,900,000
Pooled Trust Preferred Securities, Not Subject to FASB ASC 325-10 [Member]
Investment [Line Items]
Number of trust preferred securities | Security	2
Securities portfolio at fair value	$ 7,800,000
Unrealized losses	$ 6,000,000
Pooled Trust Preferred Securities, Subject To FASB ASC 325-10 [Member]
Investment [Line Items]
Number of trust preferred securities | Security	1
Securities portfolio at fair value	$ 300,000
Unrealized losses	$ 2,900,000
Pooled Trust Preferred Securities [Member]
Investment [Line Items]
Number of trust preferred securities | Security	3
Securities portfolio at fair value	$ 8,100,000
Unrealized losses	8,900,000
Unrealized losses	8,892,000	9,420,000
Other-than-temporary-impairment losses	$ 0	$ 0