Regulatory Capital - Summary of Capital Amounts, Tier 1 Risk Based and Tier 1 Leveraged Ratios (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Jan. 01, 2017	Dec. 31, 2016	Jan. 01, 2015
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 capital (to risk weighted assets), Actual Amount	$ 677,976		$ 628,139
Tier 1 capital (to risk weighted assets), Actual Amount	895,447		844,755
Total capital (to risk weighted assets), Actual Amount	1,014,784		966,097
Tier 1 capital (to average assets), Actual Amount	$ 895,447		$ 844,755
Common equity Tier 1 ( to risk weighted assets), Actual Ratio	8.284%		8.487%
Tier 1 capital (to risk weighted assets), Actual Ratio	10.941%		11.414%
Total capital (to risk weighted assets), Actual Ratio	12.399%		13.053%
Tier 1 capital (to average assets), Actual Ratio	8.355%		9.067%
Common equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 470,603		$ 379,306
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	593,369		490,322
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	757,057		638,343
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 428,709		$ 372,652
Common equity Tier 1 (to risk weighted assets), For Capital Adequacy Purposes Ratio	5.75%	5.75%	5.125%
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	7.25%	7.25%	6.625%	6.00%
Total capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	9.25%	9.25%	8.625%
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 capital (to risk weighted assets), Actual Amount	$ 1,009,380		$ 857,421
Tier 1 capital (to risk weighted assets), Actual Amount	1,009,380		857,421
Total capital (to risk weighted assets), Actual Amount	1,156,766		1,003,609
Tier 1 capital (to average assets), Actual Amount	$ 1,009,380		$ 857,421
Common equity Tier 1 ( to risk weighted assets), Actual Ratio	12.342%		11.626%
Tier 1 capital (to risk weighted assets), Actual Ratio	12.342%		11.626%
Total capital (to risk weighted assets), Actual Ratio	14.145%		13.608%
Tier 1 capital (to average assets), Actual Ratio	9.434%		9.233%
Common equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 470,242		$ 377,973
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	592,914		488,599
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	756,477		636,101
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 427,963		$ 371,466
Common equity Tier 1 (to risk weighted assets), For Capital Adequacy Purposes Ratio	5.75%	5.75%	5.125%
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	7.25%	7.25%	6.625%
Total capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	9.25%	9.25%	8.625%
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	$ 531,578		$ 479,380
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	654,250		590,006
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	817,813		737,508
Tier 1 capital (to average assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 534,954		$ 464,333
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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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 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 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.

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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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