1st Source Corporation (Parent Company Only) Financial Information (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of premises and equipment	$ 5,673	$ 5,786	$ 5,620
Amortization of right of use assets	2,842	3,046	0
Stock-based compensation	3,293	2,765	3,553
Other	940	1,734	940
Investing activities:
Net change in partnership investments	(54,981)	(33,840)	(13,669)
Financing activities:
Proceeds from issuance of long-term debt and mandatorily redeemable securities	10,000	0	0
Payments on long-term debt and mandatorily redeemable securities	(2,905)	(2,695)	(1,735)
Stock issued under stock purchase plans	39	49	145
Acquisition of treasury stock	(6,415)	(15,085)	(9,271)
Cash dividends paid on common stock	(29,764)	(29,021)	(25,686)
Parent Company
1st Source Corporation (Parent Company Only) Financial Information
Net income	81,461	92,015	82,414
Adjustments to reconcile net income to net cash provided by operating activities:
Equity (undistributed) distributed in excess of income of subsidiaries	(42,178)	(49,678)	(41,204)
Depreciation of premises and equipment	2	2	2
Amortization of right of use assets	1,107	1,350	0
Stock-based compensation	94	78	71
Realized/unrealized investment securities and other investment losses (gains)	44	(109)	180
Other	(103)	533	45
Net change in operating activities	40,427	44,191	41,508
Investing activities:
Net change in partnership investments	(182)	(260)	(980)
Payments to Acquire Businesses and Interest in Affiliates	0	(325)	0
Net change in investing activities	(182)	(585)	(980)
Financing activities:
Net change in commercial paper	774	(332)	(1,790)
Proceeds from issuance of long-term debt and mandatorily redeemable securities	1,640	1,611	1,867
Payments on long-term debt and mandatorily redeemable securities	(2,268)	(2,068)	(1,064)
Stock issued under stock purchase plans	39	49	145
Net proceeds from issuance of treasury stock	1,706	1,878	1,763
Acquisition of treasury stock	(6,415)	(15,085)	(9,271)
Cash dividends paid on common stock	(29,764)	(29,021)	(25,686)
Net change in financing activities	(34,288)	(42,968)	(34,036)
Net change in cash and cash equivalents	5,957	638	6,492
Cash and cash equivalents, beginning of year	107,285	106,647	100,155
Cash and cash equivalents, end of year	$ 113,242	$ 107,285	$ 106,647