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Regulatory Capital - Narrative (Details) | Mar. 31, 2018 | Jan. 01, 2018 | Dec. 31, 2017 | Jan. 01, 2017 | Jan. 01, 2015
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Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |
Capital conservation buffer to risk weighted assets, year one | 0.625% |  |  |  |
Capital conservation buffer to risk weighted assets, year two | 1.25% |  |  |  |
Capital conservation buffer to risk weighted assets, year three | 1.875% |  |  |  |
Capital conservation buffer to risk weighted assets, year four and thereafter | 2.50% |  |  |  |
Capital conservation buffer, excess of minimum capital ratio |  |  |  |  | 2.50%
Common equity Tier 1 (to risk weighted assets), for capital adequacy purposes ratio | 4.50% | 6.375% | 4.50% |  |
Tier 1 capital (to risk weighted assets), for capital adequacy purposes ratio | 6.00% | 7.875% | 6.00% |  |
Total capital (to risk weighted assets), for capital adequacy purposes ratio | 8.00% | 9.875% | 8.00% |  |
Customers Bank |  |  |  |  |
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items] |  |  |  |  |
Common equity Tier 1 (to risk weighted assets), for capital adequacy purposes ratio | 4.50% |  | 4.50% | 6.375% |
Tier 1 capital (to risk weighted assets), for capital adequacy purposes ratio | 6.00% |  | 6.00% | 7.875% |
Total capital (to risk weighted assets), for capital adequacy purposes ratio | 8.00% |  | 8.00% | 9.875% |

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- Definition Tier One Common Capital Required for Capital Adequacy to Risk Weighted Assets + References No definition available. + Details
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- Definition The minimum Total risk based capital ratio (total 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 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826 Reference 3: 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 + 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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