Mortgage Loan Servicing, Origination, and Loans Held for Sale (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Mortgage Loan Servicing, Origination, and Loans Held for Sale
Mortgage servicing rights	$ 85,164	$ 86,610
Changes in the fair value of MSRs and its offsetting hedge.
(Decrease)/increase in fair value of MSRs	$ (1,350)	$ 14,886	$ 9,930
Servicing Asset, Fair Value, Change in Fair Value, Valuation Input, Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax
Decay of MSRs	$ (8,540)	$ (9,897)	$ (14,863)
Gain (loss) related to derivatives	(1,420)	(18,212)	(4,892)
Net effect on Consolidated Statements of Net Income	$ (11,310)	$ (13,223)	$ (9,825)
Characteristics and sensitivity analysis of the MSR
Composition of residential loans serviced for others	100.00%	100.00%
Weighted average life (in years)	8 years 10 days	8 years 4 months 13 days
Constant Prepayment rate (CPR) (as a percent)	7.00%	6.40%
Estimated impact on fair value of a 10% increase, Constant Prepayment rate (CPR)	$ (522)	$ (129)
Estimated impact on fair value of a 20% increase, Constant Prepayment rate (CPR)	(1,014)	(266)
Estimated impact on fair value of a 10% decrease, Constant Prepayment rate (CPR)	551	118
Estimated impact on fair value of a 20% decrease, Constant Prepayment rate (CPR)	$ 1,128	$ 219
Weighted average discount rate (as a percent)	10.70%	10.00%
Estimated impact on fair value of a 10% increase, Weighted average discount rate	$ (3,270)	$ (2,554)
Estimated impact on fair value of a 20% increase, Weighted average discount rate	(6,458)	(5,321)
Estimated impact on fair value of a 10% decrease, Weighted average discount rate	3,242	2,158
Estimated impact on fair value of a 20% decrease, Weighted average discount rate	6,283	3,831
Effect on fair value due to change in interest rates:
25 basis point increase	1,647	774
50 basis point increase	3,189	1,428
25 basis point decrease	(1,723)	(902)
50 basis point decrease	$ (3,501)	$ (1,938)
Fixed-rate mortgage loans
Characteristics and sensitivity analysis of the MSR
Composition of residential loans serviced for others	100.00%	100.00%
First Financial Holdings, Inc. ("First Financial")
Mortgage Loan Servicing, Origination, and Loans Held for Sale
Residential mortgages serviced for others	$ 6,600,000	$ 6,600,000
Contractually specified servicing fees earned	$ 16,500	$ 16,200
Contractually Specified Servicing Fee Income, Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenue from Contract with Customer, Excluding Assessed Tax	Revenue from Contract with Customer, Excluding Assessed Tax
First Financial Holdings, Inc. ("First Financial") | MSRs
Analysis of the activity in the MSRs
Balance at beginning of the period	$ 86,600
Balance at end of period	$ 85,200	$ 86,600