Parent Company Only Financial Statements (Statements of Income) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Other (loss) income													$ 28,589	$ 25,918	$ 11,988
Interest expense	$ 46,651	$ 38,896	$ 32,045	$ 26,071	$ 23,257	$ 21,316	$ 17,185	$ 12,799	$ 11,969	$ 6,753	$ 5,442	$ 5,134	143,663	74,557	29,298
Operating expenses	108,366	109,661	104,561	101,610	100,022	119,539	98,237	104,196	114,302	106,144	59,085	58,887	424,198	421,994	338,418
Income tax benefit	(5,200)	(11,312)	(12,434)	(12,955)	(61,234)	(10,253)	(23,036)	(12,257)	(18,969)	(2,848)	(10,532)	(9,757)	(41,901)	(106,780)	(42,106)
Net income	$ 73,039	$ 70,397	$ 68,988	$ 71,596	$ 9,446	$ 40,459	$ 52,014	$ 47,604	$ 47,168	$ 11,484	$ 25,775	$ 23,605	284,020	149,523	108,032
Chemical Financial Corporation
Condensed Financial Statements, Captions [Line Items]
Cash dividends from subsidiaries													114,300	165,000	110,450
Other (loss) income													(269)	921	151
Total income													114,031	165,921	110,601
Interest expense													1,601	3,076	1,816
Operating expenses													13,784	23,298	30,589
Total expenses													15,385	26,374	32,405
Income before income taxes and equity in undistributed net income of subsidiaries													98,646	139,547	78,196
Income tax benefit													4,472	12,670	11,378
Equity in undistributed net income (loss) of subsidiaries													180,902	(2,694)	18,458
Net income													$ 284,020	$ 149,523	$ 108,032