1st Source Corporation (Parent Company Only) Financial Information (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of premises and equipment	$ 4,452	$ 4,596	$ 5,093
Amortization of right of use assets	3,073	3,181	3,095
Stock-based compensation	4,891	3,587	4,214
Other	(2,959)	(4,006)	279
Investing activities:
Net change in partnership investments	(51,121)	(18,292)	(24,897)
Financing activities:
Payments on long-term debt and mandatorily redeemable securities	(3,450)	(25,530)	(13,460)
Stock issued under stock purchase plans	78	252	90
Acquisition of treasury stock	(12,469)	(6,836)	(33,136)
Cash dividends paid on common stock	(33,074)	(32,102)	(31,340)
Parent Company
1st Source Corporation (Parent Company Only) Financial Information
Net income	124,934	120,532	118,557
Adjustments to reconcile net income to net cash provided by operating activities:
Equity (undistributed) distributed in excess of income of subsidiaries	(81,621)	(73,329)	(76,493)
Depreciation of premises and equipment	0	0	1
Amortization of right of use assets	1,354	1,376	1,346
Stock-based compensation	152	120	102
Realized/unrealized investment securities and other investment gains	(261)	(353)	(342)
Other	2,863	(702)	1,556
Net change in operating activities	47,421	47,644	44,727
Investing activities:
Net change in partnership investments	(246)	102	(74)
Net change in investing activities	(246)	102	(74)
Financing activities:
Net change in commercial paper	(3,096)	(871)	(800)
Proceeds from issuance of long-term debt and mandatorily redeemable securities	1,908	1,862	1,738
Payments on long-term debt and mandatorily redeemable securities	(2,887)	(2,708)	(2,427)
Stock issued under stock purchase plans	78	252	90
Net proceeds from issuance of treasury stock	3,576	2,792	2,523
Acquisition of treasury stock	(12,469)	(6,836)	(33,136)
Cash dividends paid on common stock	(33,074)	(32,102)	(31,340)
Net change in financing activities	(45,964)	(37,611)	(63,352)
Net change in cash and cash equivalents	1,211	10,135	(18,699)
Cash and cash equivalents, beginning of year	104,678	94,543	113,242
Cash and cash equivalents, end of year	$ 105,889	$ 104,678	$ 94,543