Parent Company Only Financial Statements (Financial Position) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets
Premises and equipment	$ 123,442	$ 126,896
Goodwill	1,134,568	1,134,568
Other assets	754,167	709,154
Total assets	21,498,341	19,280,873
Liabilities and Equity [Abstract]
Other liabilities	225,110	181,203
Total liabilities	18,662,081	16,612,124
Shareholders' equity	2,836,260	2,668,749	$ 2,581,526	$ 1,015,974
Total liabilities and shareholders' equity	21,498,341	19,280,873
Chemical Financial Corporation
Assets
Cash at subsidiary bank	11,477	5,761
Investment in subsidiaries	2,820,866	2,673,858
Premises and equipment	3,595	3,931
Goodwill	1,092	1,092
Deferred tax asset	5,865	7,203
Other assets	27,157	31,459
Total assets	2,870,052	2,723,304
Liabilities and Equity [Abstract]
Other liabilities	17,892	18,877
Non-revolving line-of-credit	0	19,963
Subordinated debentures	15,900	15,715
Total liabilities	33,792	54,555
Shareholders' equity	2,836,260	2,668,749
Total liabilities and shareholders' equity	$ 2,870,052	$ 2,723,304