1st Source Corporation (Parent Company Only) Financial Information (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating activities:
Net income	$ 57,786	$ 57,486	$ 58,069
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of premises and equipment	5,245	4,780	4,748
Stock-based compensation	2,884	3,843	3,179
Change in trading account securities	0	205	(13)
Other	450	3,168	2,733
Net change in operating activities	98,060	100,608	72,351
Investing activities:
Proceeds from liquidation of partnership investment	2,903	423	570
Net change in investing activities	(309,847)	(381,613)	(128,827)
Financing activities:
Proceeds from issuance of long-term debt and mandatorily redeemable securities	20,837	0	7,161
Payments on long-term debt and mandatorily redeemable securities	(6,429)	(1,250)	(11,660)
Stock issued under stock purchase plans	120	149	197
Acquisition of treasury stock	(8,030)	(9,970)	(16,342)
Cash dividends paid on common stock	(19,416)	(18,126)	(17,643)
Net change in financing activities	240,370	294,536	42,614
Net change in cash and cash equivalents	28,583	13,531	(13,862)
Cash and cash equivalents, beginning of year	79,721	66,190	80,052
Cash and cash equivalents, end of year	108,304	79,721	66,190
Parent Company
Operating activities:
Net income	57,786	57,486	58,069
Adjustments to reconcile net income to net cash provided by operating activities:
Equity (undistributed) distributed in excess of income of subsidiaries	(22,885)	(24,620)	(29,182)
Depreciation of premises and equipment	4	9	21
Stock-based compensation	52	64	35
Realized/unrealized investment securities and other investment (gains) losses	(3,901)	(26)	370
Change in trading account securities	0	205	(13)
Other	3,132	2,585	(2,329)
Net change in operating activities	34,188	35,703	26,971
Investing activities:
Proceeds from sales and maturities of investment securities	1,795	1,470	0
Proceeds from liquidation of partnership investment	2,903	423	570
Return of capital from subsidiaries	0	0	1,500
Net change in investing activities	4,698	1,893	2,070
Financing activities:
Net change in commercial paper	(2,281)	(4,126)	(183)
Proceeds from issuance of long-term debt and mandatorily redeemable securities	1,607	1,520	1,356
Payments on long-term debt and mandatorily redeemable securities	(627)	(712)	(569)
Stock issued under stock purchase plans	120	149	197
Net proceeds from issuance of treasury stock	2,636	2,373	1,520
Acquisition of treasury stock	(8,030)	(9,970)	(16,342)
Cash dividends paid on common stock	(19,416)	(18,126)	(17,643)
Net change in financing activities	(25,991)	(28,892)	(31,664)
Net change in cash and cash equivalents	12,895	8,704	(2,623)
Cash and cash equivalents, beginning of year	60,429	51,725	54,348
Cash and cash equivalents, end of year	$ 73,324	$ 60,429	$ 51,725