1st Source Corporation (Parent Company Only) Financial Information (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
ASSETS
Operating lease right of use assets	$ 21,692	$ 20,916
Other assets	427,779	380,010
Investment carrying amount	8,727,958	8,339,416
LIABILITIES AND SHAREHOLDERS' EQUITY
Long-term debt and mandatorily redeemable securities	47,911	46,555
Subordinated notes	58,764	58,764
Operating lease liabilities	19,413	19,634
Other liabilities	202,080	166,537
Unfunded capital and other commitments	7,659,695	7,415,650
Total shareholders’ equity	989,568	864,068
Total liabilities and shareholders’ equity	8,727,958	8,339,416
Parent
ASSETS
Cash and cash equivalents	105,889	104,678	$ 94,543	$ 113,242
Operating lease right of use assets	13,895	14,730
Other assets	6,821	6,234
Investment carrying amount	1,092,794	968,850
LIABILITIES AND SHAREHOLDERS' EQUITY
Commercial paper	0	3,096
Long-term debt and mandatorily redeemable securities	27,158	25,240
Subordinated notes	58,764	58,764
Operating lease liabilities	11,682	13,509
Other liabilities	5,622	4,173
Unfunded capital and other commitments	103,226	104,782
Total shareholders’ equity	989,568	864,068
Total liabilities and shareholders’ equity	1,092,794	968,850
Parent | Bank subsidiaries
ASSETS
Short-term investments with bank subsidiary	500	500
Investments in subsidiary	965,688	842,707
Parent | Non-bank subsidiaries
ASSETS
Investments in subsidiary	$ 1	$ 1