Regulatory Capital - Summary of Capital Amounts, Tier 1 Risk Based and Tier 1 Leveraged Ratios (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 capital (to risk weighted assets), Actual Amount	$ 1,082,396	$ 954,839
Tier 1 capital (to risk weighted assets), Actual Amount	1,299,867	1,172,310
Total capital (to risk weighted assets), Actual Amount	1,502,069	1,401,119
Tier 1 capital (to average assets), Actual Amount	$ 1,299,867	$ 1,172,310
Common equity Tier 1 (to risk weighted assets), Actual Ratio	9.56%	8.079%
Tier 1 capital (to risk weighted assets), Actual Ratio	0.11481	0.09919
Total capital (to risk weighted assets), Actual Ratio	0.13267	0.11855
Tier 1 capital (to average assets), Actual Ratio	0.08389	0.08597
Common equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 509,472	$ 531,844
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	679,296	709,125
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	905,729	945,500
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 619,832	$ 545,485
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	0.06000	0.06000
Total capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	0.08000	0.08000
Tier 1 capital (to average assets), For Capital Adequacy Purposes Ratio	0.04000	0.04000
Common equity Tier 1 (to risk weighted assets), for Basel III amount	$ 792,512	$ 827,312
Tier 1 (to risk weighted assets) Required for Basel III amount	962,337	1,004,594
Total capital (to risk weighted assets), for Basel III amount	1,188,769	1,240,969
Tier 1 (to risk average assets), for Basel III amount	$ 619,832	$ 545,485
Common equity Tier 1 (to risk weighted assets), for Basel III ratio	7.00%	7.00%
Tier 1 capital (to risk weighted assets), for Basel III ratio	8.50%	8.50%
Total capital (to risk weighted assets), for Basel III ratio	10.50%	10.50%
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	$ 1,403,324	$ 1,254,082
Tier 1 capital (to risk weighted assets), Actual Amount	1,403,324	1,254,082
Total capital (to risk weighted assets), Actual Amount	1,559,161	1,424,791
Tier 1 capital (to average assets), Actual Amount	$ 1,403,324	$ 1,254,082
Common equity Tier 1 (to risk weighted assets), Actual Ratio	12.395%	10.615%
Tier 1 capital (to risk weighted assets), Actual Ratio	0.12395	0.10615
Total capital (to risk weighted assets), Actual Ratio	0.13772	0.12060
Tier 1 capital (to average assets), Actual Ratio	0.09070	0.09208
Common equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 509,460	$ 531,639
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	679,279	708,852
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	905,706	945,136
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 618,871	$ 544,758
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	0.06000	0.06000
Total capital (to risk weighted assets), For Capital Adequacy Purposes Ratio	0.08000	0.08000
Tier 1 capital (to average assets), For Capital Adequacy Purposes Ratio	0.04000	0.04000
Common equity Tier 1 Capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 735,886	$ 767,923
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	905,706	945,136
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	1,132,132	1,181,421
Tier 1 capital (to average assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 773,589	$ 680,947
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	0.08000	0.08000
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	0.10000	0.10000
Tier 1 capital (to average assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Ratio	0.05000	0.05000
Common equity Tier 1 (to risk weighted assets), for Basel III amount	$ 792,493	$ 826,994
Tier 1 (to risk weighted assets) Required for Basel III amount	962,313	1,004,207
Total capital (to risk weighted assets), for Basel III amount	1,188,739	1,240,492
Tier 1 (to risk average assets), for Basel III amount	$ 618,871	$ 544,758
Common equity Tier 1 (to risk weighted assets), for Basel III ratio	7.00%	7.00%
Tier 1 capital (to risk weighted assets), for Basel III ratio	8.50%	8.50%
Total capital (to risk weighted assets), for Basel III ratio	10.50%	10.50%
Tier 1 capital (to average assets), for Basel III ratio	4.00%	4.00%