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Conversion calculation percentage.

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Share based compensation arrangement by share based payment award earned under return on average assets in period.

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Share based compensation arrangement by share based payment award equity instruments other than options expected to vest grants in period.

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Share based compensation arrangement by share based payment award maximum target percentage of performance shares of assets on peer group.

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Share based compensation arrangement by share based payment award percentage of target number of shares to be earned.

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Share based compensation arrangement by share based payment award shares vested number of shares.

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Aggregate number of common shares reserved for future issuance.

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Face amount or stated value per share of common stock.

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Amount of tax benefit from exercise of option under share-based payment arrangement.

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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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Amount of cash inflow from exercise of option under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of options vested.

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Total number of shares issued during the period, including shares forfeited, as a result of Restricted Stock Awards.

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Share-Based Compensation - Additional Information (Details) - USD ($)					1 Months Ended		3 Months Ended							9 Months Ended		12 Months Ended
	May 15, 2019	Apr. 30, 2019	Oct. 03, 2017	Jul. 06, 2017	Feb. 29, 2020	Oct. 31, 2014	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, voting par value							$ 0.01			$ 0.01				$ 0.01		$ 0.01
Proceeds from the exercise of stock options														$ 2,548,000	$ 2,359,000
Oak Park River Forest Bankshares, Inc.
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Consideration paid in cash	$ 4,200,000	$ 6,163,000
Business combination conversion of outstanding options	35,870
Performance Options Grants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options vested			414,894
Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock in connection with restricted stock awards, shares							(5,886)		174,036	16,345	36,350	136,469	(8,500)
Number of options exercised							165,375	5,196	55,402	71,029	3,472	116,048	50,662
Common Stock \| Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of restricted voting common stock granted					175,493
Common stock, voting par value					$ 0.01
Shares vested																5,254
Common Stock \| Restricted Shares \| Each Anniversary of Grant Date Over Four Years
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period					4 years
Shares vest on grant date					104,779
Common Stock \| Restricted Shares \| Each Anniversary of Grant Date Vest Over Three Years
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period					3 years
Shares vest on grant date					38,786
Omnibus Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common stock reserved for issuance																					1,550,000
Number of common shares available for future grants							1,001,731							1,001,731
Omnibus Plan \| Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period																		4 years
Shares of restricted voting common stock granted														175,493
Restricted shares vested														104,364		48,491
Fair value of restricted shares, vested														$ 1,200,000		$ 900,000
Fair value of unvested restricted stock awards							$ 4,400,000							$ 4,400,000
Omnibus Plan \| Performance-based Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of restricted voting common stock granted					31,928											20,975	11,165
Period for number of shares earned under return on average assets					3 years											3 years	3 years
Minimum target percentage in assets of peer group consisting publicly-traded bank holding companies																	50.00%
Maximum target percentage in assets of peer group consisting publicly-traded bank holding companies																	200.00%
Omnibus Plan \| Performance-based Restricted Shares \| Threshold performance
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of target number of shares to be earned																	25.00%
Omnibus Plan \| Performance-based Restricted Shares \| 50th Percentile Performance
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of target number of shares to be earned																	100.00%
Omnibus Plan \| Performance-based Restricted Shares \| 75th Percentile Performance
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of target number of shares to be earned																	125.00%
Omnibus Plan \| Common Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Issuance of common stock in connection with restricted stock awards, shares				58,900														11,898
Omnibus Plan \| Common Stock \| Restricted Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of restricted voting common stock granted																210,622	131,157
Common stock, voting par value										$ 0.01						$ 0.01	$ 0.01
Shares vested																	4,053
Omnibus Plan \| Common Stock \| Restricted Shares \| Each Anniversary of Grant Date Over Four Years
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period																4 years	4 years
Shares vest on grant date																111,823	101,559
Omnibus Plan \| Common Stock \| Restricted Shares \| Each Anniversary of Grant Date Vest Over Three Years
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period																3 years	3 years
Shares vest on grant date																72,570	14,380
BYB Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares available for future grants																					0
Number of options granted																		0	212,400	1,634,568
Number of shares outstanding							1,390,579			1,410,075				1,390,579		1,410,075
Options vested														20,000
Number of options exercised														19,496		127,997
Proceeds from the exercise of stock options														$ 253,000		$ 1,900,000
Tax benefit from exercise of stock options														$ 39,000		$ 145,000
BYB Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of common shares available for future grants						2,476,122
BYB Plan \| Time Options Grants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award contractual term						10 years
BYB Plan \| Time Options Grants \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period						5 years
BYB Plan \| Time Options Grants \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period						1 year
BYB Plan \| Performance Options Grants
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award contractual term						10 years
BYB Plan \| Performance Options Grants \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period						5 years
BYB Plan \| Performance Options Grants \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting period						1 year
FEB Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares outstanding							285,792			511,169				285,792		511,169
Number of options exercised														206,477		113,214
Proceeds from the exercise of stock options														$ 2,300,000		$ 1,300,000
Tax benefit from exercise of stock options														$ 165,000		$ 253,000
Conversion calculation percentage							472.50%							472.50%