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Stockholders' Equity and Regulatory Capital (Regulatory Capital Ratios) (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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Compliance with Regulatory Capital Requirements under Banking Regulations |  |
Total Capital | $ 214,501 | $ 204,117
Total Capital to Risk-Weighted Assets | 11.98% | 11.74%
Total Capital, Minimum Required for Capital Adequacy Purposes | $ 143,219 | $ 139,101
Total Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes | 8.00% | 8.00%
Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 165,597 | $ 149,968
Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 9.25% | 8.625%
Tier 1 capital | $ 169,176 | $ 160,964
Tier 1 Capital to Risk-Weighted Assets | 9.45% | 9.26%
Tier 1 Capital, Minimum Required for Capital Adequacy Purposes | $ 107,414 | $ 104,326
Tier 1 Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes | 6.00% | 6.00%
Tier One Risk Based Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 129,792 | $ 115,193
Tier One Risk Based Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 7.25% | 6.625%
Common Equity Tier One Capital | $ 159,157 | $ 150,960
Common Equity Tier One Capital to Risk-Weighted Assets | 8.89% | 8.68%
Common Equity Tier One Capital Required for Capital Adequacy | $ 80,561 | $ 78,244
Common Equity Tier One Capital Required for Capital Adequacy to Risk-Weighted Assets | 4.50% | 4.50%
Common Equity Tier One Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 102,939 | $ 89,111
Common Equity Tier One Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 5.75% | 5.125%
Tier 1 Capital | $ 169,176 | $ 160,964
Tier 1 Capital to Average Assets | 9.54% | 9.07%
Tier 1 Leverage Capital, Minimum Required for Capital Adequacy Purposes | $ 70,920 | $ 70,985
Tier 1 Leverage Capital to Average Assets, Minimum Required for Capital Adequacy Purposes | 4.00% | 4.00%
Tier One Leverage Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 70,920 | $ 70,985
Tier One Leverage Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 4.00% | 4.00%
First Business Bank |  |
Compliance with Regulatory Capital Requirements under Banking Regulations |  |
Total Capital | $ 207,986 | $ 147,811
Total Capital to Risk-Weighted Assets | 11.66% | 11.55%
Total Capital, Minimum Required for Capital Adequacy Purposes | $ 142,736 | $ 102,362
Total Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes | 8.00% | 8.00%
Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 165,038 | $ 110,360
Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 9.25% | 8.625%
Total Capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements | $ 178,420 | $ 127,953
Total Capital to Risk-Weighted Assets, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements | 10.00% | 10.00%
Tier 1 capital | $ 186,374 | $ 134,208
Tier 1 Capital to Risk-Weighted Assets | 10.45% | 10.49%
Tier 1 Capital, Minimum Required for Capital Adequacy Purposes | $ 107,052 | $ 76,772
Tier 1 Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes | 6.00% | 6.00%
Tier One Risk Based Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 129,354 | $ 84,769
Tier One Risk Based Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 7.25% | 6.625%
Tier 1 Capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements | $ 142,736 | $ 102,362
Tier 1 Capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements | 8.00% | 8.00%
Common Equity Tier One Capital | $ 186,374 | $ 134,208
Common Equity Tier One Capital to Risk-Weighted Assets | 10.45% | 10.49%
Common Equity Tier One Capital Required for Capital Adequacy | $ 80,289 | $ 57,579
Common Equity Tier One Capital Required for Capital Adequacy to Risk-Weighted Assets | 4.50% | 4.50%
Common Equity Tier One Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 102,591 | $ 65,576
Common Equity Tier One Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 5.75% | 5.125%
Common Equity Tier One Capital to be Well Capitalized | $ 115,973 | $ 83,170
Common Equity Tier One Capital Required to be Well Capitalized to Risk-Weighted Assets | 6.50% | 6.50%
Tier 1 Capital | $ 186,374 | $ 134,208
Tier 1 Capital to Average Assets | 10.56% | 10.40%
Tier 1 Leverage Capital, Minimum Required for Capital Adequacy Purposes | $ 70,617 | $ 51,600
Tier 1 Leverage Capital to Average Assets, Minimum Required for Capital Adequacy Purposes | 4.00% | 4.00%
Tier One Leverage Capital Required for Capital Adequacy Plus Capital Conservation Buffer | $ 70,617 | $ 51,600
Tier One Leverage Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets | 4.00% | 4.00%
Tier 1 Leverage Capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements | $ 88,272 | $ 64,500
Tier 1 Leverage Capital to Average Assets, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements | 5.00% | 5.00%
First Business Bank – Milwaukee |  |
Compliance with Regulatory Capital Requirements under Banking Regulations |  |
Total Capital |  | $ 24,347
Total Capital to Risk-Weighted Assets |  | 11.02%
Total Capital, Minimum Required for Capital Adequacy Purposes |  | $ 17,680
Total Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes |  | 8.00%
Capital Required for Capital Adequacy Plus Capital Conservation Buffer |  | $ 19,062
Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets |  | 8.625%
Total Capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements |  | $ 22,101
Total Capital to Risk-Weighted Assets, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements |  | 10.00%
Tier 1 capital |  | $ 22,323
Tier 1 Capital to Risk-Weighted Assets |  | 10.10%
Tier 1 Capital, Minimum Required for Capital Adequacy Purposes |  | $ 13,260
Tier 1 Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes |  | 6.00%
Tier One Risk Based Capital Required for Capital Adequacy Plus Capital Conservation Buffer |  | $ 14,642
Tier One Risk Based Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets |  | 6.625%
Tier 1 Capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements |  | $ 17,680
Tier 1 Capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements |  | 8.00%
Common Equity Tier One Capital |  | $ 22,323
Common Equity Tier One Capital to Risk-Weighted Assets |  | 10.10%
Common Equity Tier One Capital Required for Capital Adequacy |  | $ 9,945
Common Equity Tier One Capital Required for Capital Adequacy to Risk-Weighted Assets |  | 4.50%
Common Equity Tier One Capital Required for Capital Adequacy Plus Capital Conservation Buffer |  | $ 11,327
Common Equity Tier One Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets |  | 5.125%
Common Equity Tier One Capital to be Well Capitalized |  | $ 14,365
Common Equity Tier One Capital Required to be Well Capitalized to Risk-Weighted Assets |  | 6.50%
Tier 1 Capital |  | $ 22,323
Tier 1 Capital to Average Assets |  | 9.15%
Tier 1 Leverage Capital, Minimum Required for Capital Adequacy Purposes |  | $ 9,758
Tier 1 Leverage Capital to Average Assets, Minimum Required for Capital Adequacy Purposes |  | 4.00%
Tier One Leverage Capital Required for Capital Adequacy Plus Capital Conservation Buffer |  | $ 9,758
Tier One Leverage Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets |  | 4.00%
Tier 1 Leverage Capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements |  | $ 12,198
Tier 1 Leverage Capital to Average Assets, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements |  | 5.00%
Alterra Bank |  |
Compliance with Regulatory Capital Requirements under Banking Regulations |  |
Total Capital |  | $ 31,699
Total Capital to Risk-Weighted Assets |  | 13.27%
Total Capital, Minimum Required for Capital Adequacy Purposes |  | $ 19,106
Total Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes |  | 8.00%
Capital Required for Capital Adequacy Plus Capital Conservation Buffer |  | $ 20,599
Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets |  | 8.625%
Total Capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements |  | $ 23,882
Total Capital to Risk-Weighted Assets, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements |  | 10.00%
Tier 1 capital |  | $ 28,685
Tier 1 Capital to Risk-Weighted Assets |  | 12.01%
Tier 1 Capital, Minimum Required for Capital Adequacy Purposes |  | $ 14,329
Tier 1 Capital to Risk-Weighted Assets, Minimum Required for Capital Adequacy Purposes |  | 6.00%
Tier One Risk Based Capital Required for Capital Adequacy Plus Capital Conservation Buffer |  | $ 15,822
Tier One Risk Based Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets |  | 6.625%
Tier 1 Capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements |  | $ 19,106
Tier 1 Capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements |  | 8.00%
Common Equity Tier One Capital |  | $ 28,685
Common Equity Tier One Capital to Risk-Weighted Assets |  | 12.01%
Common Equity Tier One Capital Required for Capital Adequacy |  | $ 10,747
Common Equity Tier One Capital Required for Capital Adequacy to Risk-Weighted Assets |  | 4.50%
Common Equity Tier One Capital Required for Capital Adequacy Plus Capital Conservation Buffer |  | $ 12,240
Common Equity Tier One Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets |  | 5.125%
Common Equity Tier One Capital to be Well Capitalized |  | $ 15,524
Common Equity Tier One Capital Required to be Well Capitalized to Risk-Weighted Assets |  | 6.50%
Tier 1 Capital |  | $ 28,685
Tier 1 Capital to Average Assets |  | 10.58%
Tier 1 Leverage Capital, Minimum Required for Capital Adequacy Purposes |  | $ 10,842
Tier 1 Leverage Capital to Average Assets, Minimum Required for Capital Adequacy Purposes |  | 4.00%
Tier One Leverage Capital Required for Capital Adequacy Plus Capital Conservation Buffer |  | $ 10,842
Tier One Leverage Capital Required for Capital Adequacy Plus Conservation Buffer to Risk Weighted Assets |  | 4.00%
Tier 1 Leverage Capital, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements |  | $ 13,552
Tier 1 Leverage Capital to Average Assets, Minimum Required to be Well Capitalized Under Prompt Corrective Action Requirements |  | 5.00%

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- Definition The minimum amount of Tier 1 Risk Based Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826 + Details
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- Definition The minimum Tier One Capital Ratio (Tier one capital divided by risk-weighted assets) required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958570-112826 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826 + Details
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- Definition The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826 + Details
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- Definition The Tier 1 capital ratio (Tier 1 capital divided by risk weighted assets) required to be categorized as "well capitalized" under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826 + Details
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