1st Source Corporation (Parent Company Only) Financial Information (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Cash and cash equivalents	$ 83,365	$ 99,079	$ 78,033	$ 108,304
Operating lease right of use assets	24,147
Other assets	227,990	159,271
Total assets	6,622,776	6,293,745
LIABILITIES AND SHAREHOLDERS' EQUITY
Long-term debt and mandatorily redeemable securities	71,639	71,123
Subordinated notes	58,764	58,764
Operating lease liabilities	24,319
Other liabilities	140,518	78,602
Total liabilities	5,774,140	5,530,155
Total shareholders’ equity	828,277	762,082
Total liabilities and shareholders’ equity	6,622,776	6,293,745
Parent
ASSETS
Cash and cash equivalents	107,285	106,647	$ 100,155	$ 73,324
Operating lease right of use assets	17,106	0
Other assets	4,442	4,191
Total assets	935,526	852,036
LIABILITIES AND SHAREHOLDERS' EQUITY
Commercial paper	3,993	4,325
Long-term debt and mandatorily redeemable securities	25,819	24,676
Subordinated notes	58,764	58,764
Operating lease liabilities	17,329	0
Other liabilities	1,344	2,189
Total liabilities	107,249	89,954
Total shareholders’ equity	828,277	762,082
Total liabilities and shareholders’ equity	935,526	852,036
Parent | Bank subsidiaries
ASSETS
Short-term investments with bank subsidiary	500	500
Investments in subsidiary	806,192	740,697
Parent | Non-bank subsidiaries
ASSETS
Investments in subsidiary	$ 1	$ 1