Regulatory Capital - Summary of Capital Amounts, Tier 1 Risk Based and Tier 1 Leveraged Ratios (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity Tier 1 (to risk-weighted-assets), actual amount	$ 821,810	$ 745,795
Tier 1 capital (to risk-weighted assets), actual amount	1,039,281	963,266
Total capital (to risk-weighted assets), actual amount	1,256,309	1,081,962
Tier 1 capital (to average assets), actual amount	$ 1,039,281	$ 963,266
Common equity Tier 1 (to risk-weighted assets), actual ratio	7.984%	8.964%
Tier 1 capital (to risk-weighted assets), actual ratio	10.096%	11.578%
Total capital (to risk-weighted assets), actual ratio	12.205%	13.005%
Tier 1 capital (to average assets), actual ratio	9.258%	9.665%
Common equity Tier 1 (to risk-weighted assets), for capital adequacy purposes amount	$ 463,211	$ 374,388
Tier 1 capital (to risk-weighted assets), for capital adequacy purposes amount	617,615	499,185
Total capital (to risk-weighted assets), for capital adequacy purposes amount	823,487	655,580
Tier 1 capital (to average assets), for capital adequacy purposes amount	$ 449,026	$ 398,668
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	$ 720,551	$ 530,384
Tier 1 (to risk-weighted assets), for Basel III amount	874,955	655,180
Total capital (to risk-weighted assets), for Basel III amount	1,080,827	821,575
Tier 1 capital (to average assets) for Basel III amount	$ 449,026	$ 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 (to risk-weighted-assets), actual amount	$ 1,164,652	$ 1,066,121
Tier 1 capital (to risk-weighted assets), actual amount	1,164,652	1,066,121
Total capital (to risk-weighted assets), actual amount	1,330,155	1,215,522
Tier 1 capital (to average assets), actual amount	$ 1,164,652	$ 1,066,121
Common equity Tier 1 (to risk-weighted assets), actual ratio	11.323%	12.822%
Tier 1 capital (to risk-weighted assets), actual ratio	11.323%	12.822%
Total capital (to risk-weighted assets), actual ratio	12.933%	14.619%
Tier 1 capital (to average assets), actual ratio	10.379%	10.699%
Common equity Tier 1 (to risk-weighted assets), for capital adequacy purposes amount	$ 462,842	$ 374,160
Tier 1 capital (to risk-weighted assets), for capital adequacy purposes amount	617,122	498,879
Total capital (to risk-weighted assets), for capital adequacy purposes amount	822,829	665,173
Tier 1 capital (to average assets), for capital adequacy purposes amount	$ 448,851	$ 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 (to risk-weighted assets), to be well capitalized under prompt correction action provisions amount	$ 668,549	$ 540,453
Tier 1 capital (to risk-weighted assets), to be well capitalized under prompt corrective action provisions amount	822,829	665,173
Total capital (to risk-weighted assets), to be well capitalized under prompt corrective action provisions amount	1,028,537	831,466
Tier 1 capital (to average assets), to be well capitalized under prompt corrective action provisions amount	$ 561,064	$ 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	$ 719,976	$ 530,059
Tier 1 (to risk-weighted assets), for Basel III amount	874,256	654,779
Total capital (to risk-weighted assets), for Basel III amount	1,079,964	821,072
Tier 1 capital (to average assets) for Basel III amount	$ 448,851	$ 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%