Parent Company Only Financial Statements Statements of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Net Income	$ 25,504	$ 24,467	$ 19,024	$ 17,835	$ 15,305	$ 16,767	$ 16,236	$ 13,813	$ 86,830	$ 62,121	$ 56,808
Net Cash Provided by (Used in) Operating Activities [Abstract]
Share-based compensation expense									3,478	2,931	2,854
Depreciation of premises and equipment									11,028	8,980	8,713
Net Cash Provided by Operating Activities									102,982	89,931	89,679
Net Cash Provided by (Used in) Investing Activities [Abstract]
Payments to Acquire Businesses, Net of Cash Acquired									16,551	(14,260)	0
Purchase of investment securities available-for-sale									0	0	(304,264)
Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities									239,179	165,749	154,959
Purchases of premises and equipment, net									(8,527)	(13,411)	(8,664)
Net Cash Used in Investing Activities									(408,717)	(478,755)	(648,475)
Net Cash Provided by (Used in) Financing Activities [Abstract]
Payments of Ordinary Dividends, Common Stock									(36,918)	(29,528)	(24,521)
Proceeds from issuance of common stock, net of issuance costs									0	76,175	53,925
Proceeds from (Repayments of) Other Debt									125,000	0	0
Proceeds from directors' stock purchase plan and exercise of stock options									2,473	1,242	806
Restricted Stock, Value, Shares Issued Net of Tax Withholdings									(571)	(701)	(379)
Net Cash Provided by Financing Activities									361,504	261,056	213,449
Net Increase (Decrease) in Cash and Cash Equivalents									55,769	(127,768)	(345,347)
Cash and Cash Equivalents at Beginning of Year				183,020				310,788	183,020	310,788	656,135
Cash and Cash Equivalents at End of Year	238,789				183,020				238,789	183,020	310,788
Chemical Financial Corporation [Member]
Condensed Financial Statements, Captions [Line Items]
Net Income									86,830	62,121	56,808
Net Cash Provided by (Used in) Operating Activities [Abstract]
Share-based compensation expense									3,478	2,931	2,854
Gain on sale of available-for-sale investment securities									0	0	(245)
Depreciation of premises and equipment									318	327	416
Equity in undistributed net income of subsidiary bank									(35,799)	(2,498)	(35,109)
Net increase in other assets									2,873	1,101	(711)
Net increase (decrease) in other liabilities									(19,033)	(2,519)	563
Net Cash Provided by Operating Activities									38,667	61,463	24,576
Net Cash Provided by (Used in) Investing Activities [Abstract]
Payments to Acquire Businesses, Net of Cash Acquired									(45,267)	(117,853)	0
Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities									0	0	5,000
Purchases of premises and equipment, net									(320)	(26)	(9)
Net Cash Used in Investing Activities									(45,587)	(117,879)	4,991
Net Cash Provided by (Used in) Financing Activities [Abstract]
Payments of Ordinary Dividends, Common Stock									(36,918)	(29,528)	(24,521)
Proceeds from issuance of common stock, net of issuance costs									0	76,175	53,925
Repayments of Subordinated Debt									0	10,310	0
Proceeds from (Repayments of) Other Debt									25,000	0	0
Proceeds from directors' stock purchase plan and exercise of stock options									2,473	1,242	806
Restricted Stock, Value, Shares Issued Net of Tax Withholdings									(571)	(701)	(379)
Net Cash Provided by Financing Activities									(10,016)	36,878	29,831
Net Increase (Decrease) in Cash and Cash Equivalents									(16,936)	(19,538)	59,398
Cash and Cash Equivalents at Beginning of Year				$ 45,820				$ 65,358	45,820	65,358	5,960
Cash and Cash Equivalents at End of Year	$ 28,884				$ 45,820				$ 28,884	$ 45,820	$ 65,358