1st Source Corporation (Parent Company Only) Financial Information (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of premises and equipment	$ 5,786	$ 5,620	$ 5,658
Amortization of right of use assets	3,046	0	0
Stock-based compensation	2,765	3,553	2,963
Other	1,734	940	2,670
Investing activities:
Net change in partnership investments	(33,840)	(13,669)	(24,489)
Financing activities:
Proceeds from issuance of long-term debt and mandatorily redeemable securities	0	0	19,999
Payments on long-term debt and mandatorily redeemable securities	(2,695)	(1,735)	(26,628)
Stock issued under stock purchase plans	49	145	153
Acquisition of treasury stock	(15,085)	(9,271)	(41)
Cash dividends paid on common stock	(29,021)	(25,686)	(20,431)
Cash and cash equivalents, beginning of year	99,079	78,033	108,304
Cash and cash equivalents, end of year	83,365	99,079	78,033
Parent Company
1st Source Corporation (Parent Company Only) Financial Information
Net income	92,015	82,414	68,051
Adjustments to reconcile net income to net cash provided by operating activities:
Equity (undistributed) distributed in excess of income of subsidiaries	(49,678)	(41,204)	(28,872)
Depreciation of premises and equipment	2	2	2
Amortization of right of use assets	1,350	0	0
Stock-based compensation	78	71	48
Realized/unrealized investment securities and other investment (gains) losses	(109)	180	(6,431)
Other	533	45	4,122
Net change in operating activities	44,191	41,508	36,920
Investing activities:
Proceeds from sales and maturities of investment securities	0	0	6,327
Net change in partnership investments	(260)	(980)	(62)
Payments to Acquire Businesses and Interest in Affiliates	(325)	0	0
Return of capital from subsidiaries	0	0	854
Net change in investing activities	(585)	(980)	7,119
Financing activities:
Net change in commercial paper	(332)	(1,790)	354
Proceeds from issuance of long-term debt and mandatorily redeemable securities	1,611	1,867	1,248
Payments on long-term debt and mandatorily redeemable securities	(2,068)	(1,064)	(667)
Stock issued under stock purchase plans	49	145	153
Net proceeds from issuance of treasury stock	1,878	1,763	2,176
Acquisition of treasury stock	(15,085)	(9,271)	(41)
Cash dividends paid on common stock	(29,021)	(25,686)	(20,431)
Net change in financing activities	(42,968)	(34,036)	(17,208)
Net change in cash and cash equivalents	638	6,492	26,831
Cash and cash equivalents, beginning of year	106,647	100,155	73,324
Cash and cash equivalents, end of year	$ 107,285	$ 106,647	$ 100,155