Regulatory Matters - Summary of Capital Amounts, Tier 1 Risk Based and Tier 1 Leveraged Ratios (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Jan. 01, 2016
Customers Bancorp, Inc.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 (to risk-weighted-assets), actual amount	$ 745,795		$ 689,494
Tier 1 capital (to risk-weighted assets), actual amount	963,266		906,963
Total capital (to risk-weighted assets), actual amount	1,081,962		1,021,601
Tier 1 capital (to average assets), actual amount	$ 963,266		$ 906,963
Common equity Tier 1 (to risk-weighted assets), actual ratio	8.964%		8.805%
Tier 1 capital (to risk-weighted assets), actual ratio	11.578%		11.583%
Total capital (to risk-weighted assets), actual ratio	13.005%		13.047%
Tier 1 capital (to average assets), actual ratio	9.665%		8.937%
Common equity Tier 1 (to risk-weighted assets), for capital adequacy purposes amount	$ 374,388		$ 352,368
Tier 1 capital (to risk-weighted assets), for capital adequacy purposes amount	499,185		469,824
Total capital (to risk-weighted assets), for capital adequacy purposes amount	665,580		626,432
Tier 1 capital (to average assets), for capital adequacy purposes amount	$ 398,668		$ 405,949
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%
Tier 1 capital (to average assets), for capital adequacy purposes ratio	4.00%		4.00%
Common equity Tier 1 (to risk-weighted assets), for Basel III amount	$ 530,384		$ 450,248
Tier 1 (to risk-weighted assets), for Basel III amount	655,180		567,704
Total capital (to risk-weighted assets), for Basel III amount	821,575		724,313
Tier 1 capital (to average assets) for Basel III amount	$ 398,668		$ 405,949
Common equity Tier 1 (to risk-weighted assets), for Basel III ratio	6.375%		5.75%
Tier 1 capital (to risk-weighted assets), for Basel III ratio	7.875%		7.25%
Total capital (to risk-weighted assets), for Basel III ratio	9.875%		9.25%
Tier 1 capital (to average assets), for Basel III ratio	4.00%		4.00%
Customers Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 (to risk-weighted-assets), actual amount	$ 1,066,121		$ 1,023,564
Tier 1 capital (to risk-weighted assets), actual amount	1,066,121		1,023,564
Total capital (to risk-weighted assets), actual amount	1,215,522		1,170,666
Tier 1 capital (to average assets), actual amount	$ 1,066,121		$ 1,023,564
Common equity Tier 1 (to risk-weighted assets), actual ratio	12.822%		13.081%
Tier 1 capital (to risk-weighted assets), actual ratio	12.822%		13.081%
Total capital (to risk-weighted assets), actual ratio	14.619%		14.961%
Tier 1 capital (to average assets), actual ratio	10.699%		10.092%
Common equity Tier 1 (to risk-weighted assets), for capital adequacy purposes amount	$ 374,160		$ 352,122
Tier 1 capital (to risk-weighted assets), for capital adequacy purposes amount	498,879		469,496
Total capital (to risk-weighted assets), for capital adequacy purposes amount	665,173		625,994
Tier 1 capital (to average assets), for capital adequacy purposes amount	$ 398,570		$ 405,701
Common equity Tier 1 (to risk-weighted assets), for capital adequacy purposes ratio	4.50%		4.50%	5.125%
Tier 1 capital (to risk-weighted assets), for capital adequacy purposes ratio	6.00%		6.00%	6.625%
Total capital (to risk-weighted assets), for capital adequacy purposes ratio	8.00%		8.00%	8.625%
Tier 1 capital (to average assets), for capital adequacy purposes ratio	4.00%		4.00%
Common equity Tier 1 (to risk-weighted assets), to be well capitalized under prompt correction action provisions amount	$ 540,453		$ 508,621
Tier 1 capital (to risk-weighted assets), to be well capitalized under prompt corrective action provisions amount	665,173		625,994
Total capital (to risk-weighted assets), to be well capitalized under prompt corrective action provisions amount	831,466		782,493
Tier 1 capital (to average assets), to be well capitalized under prompt corrective action provisions amount	$ 498,212		$ 507,126
Common equity Tier 1 (to risk-weighted assets), to be well capitalized under prompt corrective action provisions ratio	6.50%		6.50%
Tier 1 capital (to risk-weighted assets), to be well capitalized under prompt corrective action provisions ratio	8.00%		8.00%
Total capital (to risk-weighted assets), to be well capitalized under prompt corrective action provisions ratio	10.00%		10.00%
Tier 1 capital (to average assets), to be well capitalized under prompt corrective action provisions ratio	5.00%		5.00%
Common equity Tier 1 (to risk-weighted assets), for Basel III amount	$ 530,059		$ 449,934
Tier 1 (to risk-weighted assets), for Basel III amount	654,779		567,307
Total capital (to risk-weighted assets), for Basel III amount	821,072		723,806
Tier 1 capital (to average assets) for Basel III amount	$ 398,570		$ 405,701
Common equity Tier 1 (to risk-weighted assets), for Basel III ratio	6.375%		5.75%
Tier 1 capital (to risk-weighted assets), for Basel III ratio	7.875%		7.25%
Total capital (to risk-weighted assets), for Basel III ratio	9.875%		9.25%
Tier 1 capital (to average assets), for Basel III ratio	4.00%		4.00%

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Common Equity Tier One Capital Required for Basel III

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Tier One Common Capital Required to be Well Capitalized to Risk Weighted Assets

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Tier One Leverage Capital Required for Basel III to Average Assets

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Tier One Risk Based Capital Required for Basel III

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Tier One Risk Based Capital Required for Basel III to Risk Weighted Assets

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The amount of total capital as defined in the regulations.

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The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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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.

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The amount of Total Capital required to be categorized as well as capitalized under the regulatory framework for prompt corrective action.

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The Total risk based capital ratio (total capital divided by risk weighted assets) required to be categorized as "well capitalized", in the regulatory framework for prompt corrective action.

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Total Capital divided by risk weighted assets as defined in the regulations.

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Amount of Common Equity Tier One Risk-based Capital, as defined by regulatory framework.

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Amount of Common Equity Tier 1 Risk-based Capital required to be categorized as adequately capitalized under regulatory framework for prompt corrective action.

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Amount of Common Equity Tier 1 Risk-based Capital required to be categorized as well-capitalized under regulatory framework for prompt corrective action.

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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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Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

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The minimum amount of Tier 1 Leverage Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

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The amount of Tier 1 Leverage Capital required to be categorized as well capitalized divided by average assets as defined in the regulatory framework for prompt corrective action.

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Tier 1 Leverage Capital divided by average assets as defined in the regulations.

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Tier 1 Risk Based Capital as defined in the regulations.

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The minimum amount of Tier 1 Risk Based Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action.

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The amount of Tier 1 Risk Based Capital required to be categorized as well capitalized under the regulatory framework for prompt corrective action.

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Tier 1 capital divided by risk weighted assets as defined by regulations.

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