Acquisitions - Schedule of Purchase Price of Assets Acquired and Liabilities Assumed (Detail) - USD ($)	Mar. 31, 2017	Dec. 31, 2016	Nov. 07, 2016	Sep. 30, 2016	Aug. 31, 2016	Jul. 18, 2016	Jun. 01, 2016
ASSETS
Goodwill	$ 77,644,000	$ 76,941,000
Kosciusko Financial Inc [Member]
ASSETS
Cash and due from banks							$ 38,950,000
Investment securities, available for sale							1,191,000
Total loans							102,569,000
Premises and equipment, net							1,466,000
FHLB stock							582,000
Goodwill				$ 6,400,000	$ 6,900,000		6,443,000
Core deposit intangible							526,000
Interest receivable							636,000
Cash value of life insurance							2,745,000
Other assets							765,000
Total assets purchased							155,873,000
Common shares issued							14,470,000
Cash paid							8,513,000
Total estimated purchase price							22,983,000
Deposits
Non-interest bearing							27,871,000
NOW accounts							35,213,000
Savings and money market							26,953,000
Certificates of deposits							32,771,000
Total deposits							122,808,000
Borrowings							9,038,000
Interest payable							55,000
Other liabilities							989,000
Total liabilities assumed							132,890,000
Kosciusko Financial Inc [Member] | Residential Mortgage [Member]
ASSETS
Total loans							26,244,000
Kosciusko Financial Inc [Member] | Commercial [Member]
ASSETS
Total loans							70,006,000
Kosciusko Financial Inc [Member] | Consumer [Member]
ASSETS
Total loans							$ 6,319,000
LaPorte Bancorp Inc [Member]
ASSETS
Cash and due from banks						$ 154,849,000
Investment securities, available for sale						23,779,000
Total loans						312,906,000
Premises and equipment, net						6,022,000
FHLB stock						4,029,000
Goodwill						20,993,000
Core deposit intangible						2,514,000
Interest receivable						844,000
Cash value of life insurance						15,267,000
Other assets						8,334,000
Total assets purchased						549,537,000
Common shares issued						60,306,000
Cash paid						38,328,000
Total estimated purchase price						98,634,000
Deposits
Non-interest bearing						66,733,000
NOW accounts						99,346,000
Savings and money market						117,688,000
Certificates of deposits						87,605,000
Total deposits						371,372,000
Borrowings						64,793,000
Interest payable						178,000
Subordinated debt						4,504,000
Other liabilities						10,056,000
Total liabilities assumed						450,903,000
LaPorte Bancorp Inc [Member] | Residential Mortgage [Member]
ASSETS
Total loans						42,603,000
LaPorte Bancorp Inc [Member] | Mortgage Warehousing [Member]
ASSETS
Total loans						99,752,000
LaPorte Bancorp Inc [Member] | Commercial [Member]
ASSETS
Total loans						153,750,000
LaPorte Bancorp Inc [Member] | Consumer [Member]
ASSETS
Total loans						$ 16,801,000
Central National Bank & Trust [Member]
ASSETS
Cash and due from banks			$ 27,860,000
Investment securities, available for sale			16,393,000
Total loans			10,470,000
Premises and equipment, net			444,000
FHLB stock			50,000
Goodwill			609,000
Core deposit intangible			190,000
Interest receivable			154,000
Other assets			49,000
Total assets purchased			56,219,000
Cash paid			5,311,000
Total estimated purchase price			5,311,000
Deposits
Non-interest bearing			24,079,000
NOW accounts			9,038,000
Savings and money market			13,829,000
Certificates of deposits			3,342,000
Total deposits			50,288,000
Borrowings			459,000
Interest payable			7,000
Other liabilities			154,000
Total liabilities assumed			50,908,000
Central National Bank & Trust [Member] | Residential Mortgage [Member]
ASSETS
Total loans			6,624,000
Central National Bank & Trust [Member] | Commercial [Member]
ASSETS
Total loans			2,267,000
Central National Bank & Trust [Member] | Consumer [Member]
ASSETS
Total loans			$ 1,579,000