1st Source Corporation (Parent Company Only) Financial Information (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
ASSETS
Cash and cash equivalents	$ 108,304	$ 79,721	$ 66,190	$ 80,052
Investment securities, available-for-sale (amortized cost of $884 at December 31, 2016 and $1,218 at December 31, 2015)	850,467	791,727
Other assets	130,059	129,852
Total assets	5,486,268	5,187,916
LIABILITIES AND SHAREHOLDERS' EQUITY
Long-term debt and mandatorily redeemable securities	74,308	57,379
Subordinated notes	58,764	58,764
Other liabilities	54,843	55,305
Total liabilities	4,813,618	4,543,863
Total shareholders’ equity	672,650	644,053	614,473	585,378
Total liabilities and shareholders’ equity	5,486,268	5,187,916
Available-for-sale Securities, Amortized Cost	848,316	781,232
Parent
ASSETS
Cash and cash equivalents	73,324	60,429	$ 51,725	$ 54,348
Investment securities, available-for-sale (amortized cost of $884 at December 31, 2016 and $1,218 at December 31, 2015)	7,369	6,855
Other assets	4,013	4,668
Total assets	763,933	734,035
LIABILITIES AND SHAREHOLDERS' EQUITY
Commercial paper	5,761	8,042
Long-term debt and mandatorily redeemable securities	21,228	19,335
Subordinated notes	58,764	58,764
Other liabilities	5,530	3,841
Total liabilities	91,283	89,982
Total shareholders’ equity	672,650	644,053
Total liabilities and shareholders’ equity	763,933	734,035
Available-for-sale Securities, Amortized Cost	884	1,218
Parent | Bank subsidiaries
ASSETS
Short-term investments with bank subsidiary	500	500
Investments in subsidiary	676,915	660,087
Parent | Non-bank subsidiaries
ASSETS
Investments in subsidiary	$ 1,812	$ 1,496