Regulatory Capital - Summary of Capital Amounts, Tier 1 Risk Based and Tier 1 Leveraged Ratios (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Jan. 01, 2016	Dec. 31, 2015	Jan. 01, 2015
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 (to risk weighted assets), Actual Amount	$ 553,391		$ 500,624
Tier 1 capital (to risk weighted assets), Actual Amount	770,070		556,193
Total capital (to risk weighted assets), Actual Amount	904,305		698,323
Tier 1 capital (to average assets), Actual Amount	$ 770,070		$ 556,193
Common equity Tier 1 ( to risk weighted assets), Actual Ratio	7.117%		7.61%
Tier 1 capital (to risk weighted assets), Actual Ratio	9.904%		8.46%
Total capital (to risk weighted assets), Actual Ratio	11.63%		10.62%
Tier 1 capital (to average assets), Actual Ratio	8.182%		7.16%
Common equity Tier 1 (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 398,497		$ 296,014
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	515,130		394,685
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	670,641		526,247
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 376,467		$ 310,812
Common equity Tier 1 (to risk weighted assets), For Capital Adequacy Purposes Ratio	5.125%	5.125%	4.50%
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	6.625%	6.625%	6.00%	6.00%
Total capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	8.625%	8.625%	8.00%
Tier 1 capital (to average assets), For Capital Adequacy Purposes Ratio	4.00%		4.00%
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio				8.00%
Customers Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 (to risk weighted assets), Actual Amount	$ 772,484		$ 565,217
Tier 1 capital (to risk weighted assets), Actual Amount	772,484		565,217
Total capital (to risk weighted assets), Actual Amount	919,234		710,864
Tier 1 capital (to average assets), Actual Amount	$ 772,484		$ 565,217
Common equity Tier 1 ( to risk weighted assets), Actual Ratio	9.971%		8.62%
Tier 1 capital (to risk weighted assets), Actual Ratio	9.971%		8.62%
Total capital (to risk weighted assets), Actual Ratio	11.865%		10.85%
Tier 1 capital (to average assets), Actual Ratio	8.229%		7.30%
Common equity Tier 1 (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 397,045		$ 294,916
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	513,253		393,221
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	668,198		524,295
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 375,508		$ 309,883
Common equity Tier 1 (to risk weighted assets), For Capital Adequacy Purposes Ratio	5.125%	5.125%	4.50%
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	6.625%	6.625%	6.00%
Total capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	8.625%	8.625%	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), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 503,569		$ 425,990
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	619,777		524,295
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	774,722		655,369
Tier 1 capital (to average assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 469,385		$ 387,353
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%

Tier One Common Capital Required for Capital Adequacy to Risk Weighted Assets

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

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Tier One Common Capital to Risk Weighted Assets

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Tier One Common Equity

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Tier One Common Equity Required for Capital Adequacy

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Tier One Common Equity Required to be Well Capitalized

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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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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 minimum amount of Tier 1 Leverage Capital for capital adequacy purposes divided by average assets as defined in the regulations.

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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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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.

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

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