Acquisitions - Additional Information (Detail) - USD ($)				3 Months Ended
	Feb. 03, 2017	Jul. 18, 2016	Jun. 01, 2016	Mar. 31, 2017	Dec. 31, 2016	Nov. 07, 2016	Sep. 30, 2016	Aug. 31, 2016
Business Acquisition [Line Items]
Acquisition of goodwill				$ 77,644,000	$ 76,941,000
Kosciusko Financial Inc [Member]
Business Acquisition [Line Items]
Exchange ratio per share			451.83%
Cash paid for each share			$ 81.75
Business combination stock transferred, percentage of consideration			65.00%
Business combination cash transferred, percentage of consideration			35.00%
Common stock issued			873,430
Market closing price per share			$ 16.57
Estimated transaction value			$ 23,000,000
Costs related to the acquisition			1,600,000
Acquisition of goodwill			6,443,000				$ 6,400,000	$ 6,900,000
Net intangible assets acquired			526,000
Purchase price of the business assets, portion deductible			0
Core deposit intangible amortization period				10 years
Total estimated purchase price			$ 22,983,000
Kosciusko Financial Inc [Member] | Maximum [Member]
Business Acquisition [Line Items]
Number of shares owned			100
Share of common stock outstanding per share			$ 81.75
Central National Bank & Trust [Member]
Business Acquisition [Line Items]
Acquisition of goodwill						$ 609,000
Net intangible assets acquired						190,000
Purchase price of the business assets, portion deductible						0
Core deposit intangible amortization period				10 years
Total estimated purchase price						5,311,000
Performing portion of the loan portfolio acquired						10,800,000
Estimated fair value of performing portion of the loan portfolio						$ 10,500,000
LaPorte Bancorp Inc [Member]
Business Acquisition [Line Items]
Exchange ratio per share		94.35%
Cash paid for each share		$ 17.50
Business combination stock transferred, percentage of consideration		65.00%
Business combination cash transferred, percentage of consideration		35.00%
Common stock issued		3,421,488
Market closing price per share		$ 18.36
Estimated transaction value		$ 98,600,000
Costs related to the acquisition		4,000,000
Acquisition of goodwill		20,993,000
Net intangible assets acquired		2,514,000
Purchase price of the business assets, portion deductible		0
Core deposit intangible amortization period				10 years
Total estimated purchase price		$ 98,634,000
Goodwill adjustment				$ 703,000
First Farmers Bank & Trust Co [Member]
Business Acquisition [Line Items]
Acquisition of goodwill	$ 0
Net intangible assets acquired	$ 463,000
Core deposit intangible amortization period	10 years
Payments received as cash consideration	$ 10,900,000
Business acquisition, loans assumed	$ 3,400,000
Premium on deposits paid	3.00%
Business acquisition, customer deposit balances	$ 14,800,000