Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands		Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balances (in shares) at Dec. 31, 2014			13,215,800
Beginning Balance at Dec. 31, 2014		$ 228,824	$ 13,216	$ 108,660	$ 104,058	$ 2,890
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		30,064			30,064
Other Comprehensive Income (Loss)		922				922
Cash Dividends ($.52, $.48, $.45 per share)	[1]	(9,010)			(9,010)
Issuance of Common Stock for:
Exercise of Stock Options (in shares)			12,985
Exercise of Stock Options		49	$ 13	36
Restricted Share Grants (in shares)			34,826
Restricted Share Grants		963	$ 35	928
Employee Stock Purchase Plan (in shares)			15,213
Employee Stock Purchase Plan		447	$ 15	432
Income Tax Benefit From Restricted Share Vesting		89		89
Ending Balances (in shares) at Dec. 31, 2015			13,278,824
Ending Balance at Dec. 31, 2015		252,348	$ 13,279	110,145	125,112	3,812
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		35,184			35,184
Other Comprehensive Income (Loss)		(10,216)				(10,216)
Cash Dividends ($.52, $.48, $.45 per share)	[1]	(10,630)			(10,630)
Issuance of Common Stock for:
Exercise of Stock Options (in shares)			4,166
Exercise of Stock Options		55	$ 4	51
Acquisition of River Valley Bancorp (in shares)			1,942,429
Acquisition of River Valley Bancorp		61,919	$ 1,942	59,977
Restricted Share Grants (in shares)			36,012
Restricted Share Grants		1,407	$ 36	1,371
Income Tax Benefit From Restricted Share Vesting		200		200
Ending Balances (in shares) at Dec. 31, 2016			15,261,431
Ending Balance at Dec. 31, 2016		330,267	$ 15,261	171,744	149,666	(6,404)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income		40,676			40,676
Other Comprehensive Income (Loss)		4,253				4,253
Reclass Upon Adoption of ASU 2018-02 (See Note 1 - Summary of Significant Accounting Policies)		0			469	(469)
Cash Dividends ($.52, $.48, $.45 per share)	[1]	(11,842)			(11,842)
Issuance of Common Stock for:
3-for-2 Stock Split (in shares)			7,642,726
3-for-2 Stock Split		(29)	$ 7,643	(7,672)
Restricted Share Grants (in shares)			30,246
Restricted Share Grants		1,246	$ 30	1,216
Income Tax Benefit From Restricted Share Vesting		0		0
Ending Balances (in shares) at Dec. 31, 2017			22,934,403
Ending Balance at Dec. 31, 2017		$ 364,571	$ 22,934	$ 165,288	$ 178,969	$ (2,620)

[1] Per share data has been adjusted to reflect a 3-for-2 stock split on April 21, 2017.