Mortgage Servicing Rights - Weighted-average Key Assumptions to Estimate Fair Value of MSRs (Details) - uSDPerLoan	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Transfers and Servicing [Abstract]
Discount rate	9.22%	9.12%	9.29%
Total prepayment speeds	11.52%	16.99%	13.01%
Cost of servicing each loan	85	85	86

Servicing Assets And Servicing Liabilities At Fair Value, Assumptions Used To Estimate Fair Value, Cost Of Servicing, Per Loan

No definition available.

+ Details

Name:	fcb_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueCostOfServicingPerLoan
Namespace Prefix:	fcb_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Definition

Discount rate used to estimate the fair value of servicing assets and servicing liabilities.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=125521744&loc=d3e122596-111746

+ Details

Name:	us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Estimated rate of prepayments of principal on servicing assets and servicing liabilities.

+ References

+ Details

Name:	us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValuePrepaymentSpeed
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_TransfersAndServicingAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration