1st Source Corporation (Parent Company Only) Financial Information (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income:
Operating Lease Income Comprehensive Income Extensible List Not Disclosed Flag	Rental income from subsidiaries	Rental income from subsidiaries	Rental income from subsidiaries
Other	$ 19,895	$ 15,042	$ 12,560
Expenses:
Interest on subordinated notes	4,174	3,550	3,267
Interest on long-term debt and mandatorily redeemable securities	3,892	69	2,476
Interest on commercial paper and other short-term borrowings	7,032	1,497	115
Occupancy	11,090	10,728	10,524
Other	17,433	14,287	10,902
Income before income taxes	161,680	156,787	154,885
Income tax benefit	(36,746)	(36,255)	(36,328)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	166,294	(17,320)	90,302
Parent
Income:
Rental income from subsidiaries	1,832	1,740	1,873
Other	239	148	146
Investment securities and other investment gains	261	353	342
Total income	52,484	51,829	48,568
Expenses:
Interest on subordinated notes	4,174	3,550	3,267
Interest on long-term debt and mandatorily redeemable securities	3,606	(341)	1,799
Interest on commercial paper and other short-term borrowings	2	1	3
Occupancy	1,718	1,625	1,722
Other	917	890	711
Total expenses	10,417	5,725	7,502
Income before income taxes	42,067	46,104	41,066
Income tax benefit	1,246	1,099	998
Income before equity in undistributed income of subsidiaries	43,313	47,203	42,064
Equity in undistributed income of subsidiaries	81,621	73,329	76,493
Net income	124,934	120,532	118,557
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	166,301	(17,297)	90,325
Parent | Bank subsidiaries
Income:
Dividends from bank subsidiary	50,152	49,588	46,207
Expenses:
Equity in undistributed income of subsidiaries	$ 81,621	$ 73,329	$ 76,493