Regulatory Capital - Summary of Capital Amounts, Tier 1 Risk Based and Tier 1 Leveraged Ratios (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 capital (to risk weighted assets), Actual Amount	$ 794,745		$ 745,795
Tier 1 capital (to risk weighted assets), Actual Amount	1,012,216		963,266
Total capital (to risk weighted assets), Actual Amount	1,155,499		1,081,962
Tier 1 capital (to average assets), Actual Amount	$ 1,012,216		$ 963,266
Common equity Tier 1 (to risk weighted assets), Actual Ratio	7.811%		8.964%
Tier 1 capital (to risk weighted assets), Actual Ratio	9.949%		11.578%
Total capital (to risk weighted assets), Actual Ratio	11.357%		13.005%
Tier 1 capital (to average assets), Actual Ratio	9.013%		9.665%
Common equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 457,840		$ 374,388
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	610,453		499,185
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	813,938		665,580
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 449,217		$ 398,668
Common equity Tier 1 (to risk weighted assets), For Capital Adequacy Purposes Ratio	4.50%	7.00%	4.50%
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	6.00%	8.50%	6.00%
Total capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	8.00%	10.50%	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	$ 712,195		$ 530,384
Tier 1 (to risk weighted assets) Required for Basel III amount	864,809		655,180
Total capital (to risk weighted assets), for Basel III amount	1,068,293		821,575
Tier 1 (to risk average assets), for Basel III amount	$ 449,217		$ 398,668
Common equity Tier 1 (to risk weighted assets), for Basel III ratio	7.00%		6.375%
Tier 1 capital (to risk weighted assets), for Basel III ratio	8.50%		7.875%
Total capital (to risk weighted assets), for Basel III ratio	10.50%		9.875%
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 capital (to risk weighted assets), Actual Amount	$ 1,103,341		$ 1,066,121
Tier 1 capital (to risk weighted assets), Actual Amount	1,103,341		1,066,121
Total capital (to risk weighted assets), Actual Amount	1,263,490		1,215,522
Tier 1 capital (to average assets), Actual Amount	$ 1,103,341		$ 1,066,121
Common equity Tier 1 (to risk weighted assets), Actual Ratio	10.847%		12.822%
Tier 1 capital (to risk weighted assets), Actual Ratio	10.847%		12.822%
Total capital (to risk weighted assets), Actual Ratio	12.421%		14.619%
Tier 1 capital (to average assets), Actual Ratio	9.829%		10.699%
Common equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 457,748		$ 374,160
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	610,331		498,879
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	813,775		665,173
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 448,997		$ 398,570
Common equity Tier 1 (to risk weighted assets), For Capital Adequacy Purposes Ratio	4.50%		4.50%
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	6.00%		6.00%
Total capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	8.00%		8.00%
Tier 1 capital (to average assets), For Capital Adequacy Purposes Ratio	4.00%		4.00%
Common equity Tier 1 Capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 661,192		$ 540,453
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	813,775		665,173
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	1,017,218		831,466
Tier 1 capital (to average assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 561,246		$ 498,212
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	$ 712,053		$ 530,059
Tier 1 (to risk weighted assets) Required for Basel III amount	864,636		654,779
Total capital (to risk weighted assets), for Basel III amount	1,068,079		821,072
Tier 1 (to risk average assets), for Basel III amount	$ 448,997		$ 398,570
Common equity Tier 1 (to risk weighted assets), for Basel III ratio	7.00%		6.375%
Tier 1 capital (to risk weighted assets), for Basel III ratio	8.50%		7.875%
Total capital (to risk weighted assets), for Basel III ratio	10.50%		9.875%
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 to Risk Weighted 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 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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Tier 1 Leverage Capital as defined in the regulations. Also called Core Capital.

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

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