Regulatory Capital - Summary of Capital Amounts, Tier 1 Risk Based and Tier 1 Leveraged Ratios (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 capital (to risk weighted assets), Actual Amount	$ 827,884	$ 821,810
Tier 1 capital (to risk weighted assets), Actual Amount	1,045,355	1,039,281
Total capital (to risk weighted assets), Actual Amount	1,277,340	1,256,309
Tier 1 capital (to average assets), Actual Amount	$ 1,045,355	$ 1,039,281
Common equity Tier 1 (to risk weighted assets), Actual Ratio	7.56%	7.984%
Tier 1 capital (to risk weighted assets), Actual Ratio	9.546%	10.096%
Total capital (to risk weighted assets), Actual Ratio	11.665%	12.205%
Tier 1 capital (to average assets), Actual Ratio	9.011%	9.258%
Common equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 492,760	$ 463,211
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	657,013	617,615
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	876,017	823,487
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 464,045	$ 449,026
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 (to risk weighted assets), for Basel III amount	$ 766,515	$ 720,551
Tier 1 (to risk weighted assets) Required for Basel III amount	930,768	874,955
Total capital (to risk weighted assets), for Basel III amount	1,149,773	1,080,827
Tier 1 (to risk average assets), for Basel III amount	$ 464,045	$ 449,026
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	$ 1,158,308	$ 1,164,652
Tier 1 capital (to risk weighted assets), Actual Amount	1,158,308	1,164,652
Total capital (to risk weighted assets), Actual Amount	1,334,108	1,330,155
Tier 1 capital (to average assets), Actual Amount	$ 1,158,308	$ 1,164,652
Common equity Tier 1 (to risk weighted assets), Actual Ratio	10.599%	11.323%
Tier 1 capital (to risk weighted assets), Actual Ratio	10.599%	11.323%
Total capital (to risk weighted assets), Actual Ratio	12.207%	12.933%
Tier 1 capital (to average assets), Actual Ratio	9.992%	10.379%
Common equity Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	$ 491,793	$ 462,842
Tier 1 capital (to risk weighted assets), For Capital Adequacy Purposes Amount	655,724	617,122
Total capital (to risk weighted assets), For Capital Adequacy Purposes Amount	874,298	822,829
Tier 1 capital (to average assets), For Capital Adequacy Purposes Amount	$ 463,680	$ 448,851
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	$ 710,368	$ 668,549
Tier 1 capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	874,298	822,829
Total capital (to risk weighted assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	1,092,873	1,028,537
Tier 1 capital (to average assets), To Be Well Capitalized Under Prompt Corrective Action Provisions Amount	$ 579,600	$ 561,064
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	$ 765,011	$ 719,976
Tier 1 (to risk weighted assets) Required for Basel III amount	928,942	874,256
Total capital (to risk weighted assets), for Basel III amount	1,147,517	1,079,964
Tier 1 (to risk average assets), for Basel III amount	$ 463,680	$ 448,851
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%