CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock First Community	Common Stock Mid Illinois Bancorp, Inc.	Common Stock	Additional Paid-in Capital First Community	Additional Paid-in Capital Mid Illinois Bancorp, Inc.	Additional Paid-in Capital	Accumulated (Deficit) Pulaski	Accumulated (Deficit)	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Pulaski	First Community	Mid Illinois Bancorp, Inc.	Total
Accumulated other comprehensive income (loss) beginning balance period, Net of Tax at Dec. 31, 2016			$ 39			$ 781,716		$ (163,689)	$ 36	$ (23,788)				$ 594,314
Beginning Balance (in shares) at Dec. 31, 2016			38,236,287
Increase (decrease) in shareholders' equity
Net income								62,726						62,726
Other comprehensive income (loss)									(2,846)					(2,846)
Issuance of treasury stock for employee stock purchase plan						(540)				1,016				476
Issuance of treasury stock for employee stock purchase plan (in shares)			16,842
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax						(5,521)				4,864				(657)
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax (in shares)			79,459
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax						(3,139)				3,765				626
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax (in shares)			64,941
Stock issued in acquisition of Banc Ed, net of stock issuance costs	$ 7	$ 3		$ 211,575	$ 97,594							$ 211,582	$ 97,597
Stock issued in acquisition of Banc Ed, net of stock issuance costs (in shares)	7,200,559	3,115,503
Cash dividends common stock								(30,697)						(30,697)
Stock dividend equivalents restricted stock units						452		(452)
Stock dividend accrued on restricted stock awards assumed with the Pulaski Financial Corp. acquisition at $0.54 per share							$ (10)				$ (10)
Return of equity trust shares										(860)				(860)
Return of equity trust shares (in shares)			(28,648)
Stock-based compensation						2,752								2,752
Accumulated other comprehensive income (loss) ending balance period, Net of Tax at Dec. 31, 2017			$ 49			1,084,889		(132,122)	(2,810)	(15,003)				935,003
Ending Balance (in shares) at Dec. 31, 2017			48,684,943
Increase (decrease) in shareholders' equity
Net income								98,928						98,928
Other comprehensive income (loss)									(3,397)					(3,397)
Tax Cuts and Jobs Act of 2017 reclassification								605	(605)
Issuance of treasury stock for employee stock purchase plan						(275)				811				536
Issuance of treasury stock for employee stock purchase plan (in shares)			19,442
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax						(5,930)				4,924				(1,006)
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax (in shares)			104,637
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax						(2,889)				3,078				189
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax (in shares)			65,814
Cash dividends common stock								(39,010)						(39,010)
Stock dividend equivalents restricted stock units						568		(568)
Stock-based compensation						3,721								3,721
Accumulated other comprehensive income (loss) ending balance period, Net of Tax at Dec. 31, 2018			$ 49			1,080,084		(72,167)	(6,812)	(6,190)				994,964
Ending Balance (in shares) at Dec. 31, 2018			48,874,836
Increase (decrease) in shareholders' equity
Net income								102,953						102,953
Other comprehensive income (loss)									21,772					21,772
Issuance of treasury stock for employee stock purchase plan						137				487				624
Issuance of treasury stock for employee stock purchase plan (in shares)			25,698
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax						(2,600)				382				(2,218)
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax (in shares)			92,996
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax						(104)				1,628				1,524
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax (in shares)			13,486
Stock issued in acquisition of Banc Ed, net of stock issuance costs			$ 7			166,274								166,281
Stock issued in acquisition of Banc Ed, net of stock issuance costs (in shares)			6,725,152
Repurchase of stock										(24,292)				(24,292)
Repurchase of stock (in shares)			(943,396)
Cash dividends common stock								(45,171)						(45,171)
Stock dividend equivalents restricted stock units						428		(428)
Stock-based compensation						3,997								3,997
Accumulated other comprehensive income (loss) ending balance period, Net of Tax at Dec. 31, 2019			$ 56			$ 1,248,216		$ (14,813)	$ 14,960	$ (27,985)				$ 1,220,434
Ending Balance (in shares) at Dec. 31, 2019			54,788,772