Loan Servicing, Mortgage Origination, and Loans Held for Sale (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
MSRs
Changes in the fair value of MSRs and its offsetting hedge.
Increase (decrease) in fair value of MSRs	$ (2,568,000)	$ 429,000	$ (4,924,000)	$ 2,945,000
Decay of MSRs	(1,143,000)	(1,141,000)	(2,029,000)	(2,069,000)
Gains (loss) related to derivatives	2,659,000	(339,000)	3,940,000	(1,893,000)
Net effect on statements of income	(1,052,000)	(1,051,000)	$ (3,013,000)	$ (1,017,000)
Characteristics and sensitivity analysis of the MSR
Composition of residential loans serviced for others						100.00%	100.00%	100.00%
Weighted average life (in years)			6 years 6 months 14 days	8 years 6 months 21 days	7 years 10 months 17 days
Constant Prepayment rate (CPR) (as a percent)			10.10%	6.10%	7.30%
Weighted average discount rate (as a percent)			9.40%	9.40%	9.40%
Effect on fair value due to change in interest rates:
25 basis point increase						$ 2,517,000	$ 1,504,000	$ 934,000
50 basis point increase						4,621,000	2,740,000	1,626,000
25 basis point decrease						(2,575,000)	(1,981,000)	(1,379,000)
50 basis point decrease						(5,540,000)	$ (4,421,000)	(3,112,000)
Custodial escrow balances maintained in connection with the loan servicing						$ 27,700,000		$ 26,000,000.0
Fixed-rate mortgage loans
Characteristics and sensitivity analysis of the MSR
Composition of residential loans serviced for others						99.80%	99.80%	99.70%
Adjustable-rate mortgage loans
Characteristics and sensitivity analysis of the MSR
Composition of residential loans serviced for others						0.20%	0.20%	0.30%
First Financial Holdings, Inc. ("First Financial")
Loans held for sale, loan servicing and mortgage origination
Residential mortgages serviced for others						$ 3,100,000,000	$ 3,100,000,000	$ 3,000,000,000.0
Contractually specified servicing fees earned	2,000,000.0	1,900,000	$ 3,900,000	$ 3,800,000
First Financial Holdings, Inc. ("First Financial") | MSRs
Loans held for sale, loan servicing and mortgage origination
Mortgage servicing rights	32,300,000	35,100,000	32,300,000	35,100,000	$ 34,700,000	$ 32,300,000	$ 34,700,000	$ 35,100,000
Analysis of the activity in the MSRs
Balance at beginning of the period			34,700,000
Balance at end of period	$ 32,300,000	$ 35,100,000	$ 32,300,000	$ 35,100,000	$ 34,700,000