Consolidated Statements of Equity (Unaudited) - USD ($) $ in Thousands	Total	Series B Preferred Stock	Series C Preferred Stock	Total	Total Series B Preferred Stock	Total Series C Preferred Stock	Preferred Stock	Preferred Stock Series B Preferred Stock	Common Stock	Additional Paid-in Capital	Retained Earnings	Retained Earnings Series B Preferred Stock	Retained Earnings Series C Preferred Stock	Accumulated Other Comprehensive Income (Loss)	Treasury Stock and Other	Non-controlling Interest
Increase (Decrease) in Equity
Change in accounting principle	$ (116)			$ (116)							$ (116)
Adjusted balance after cumulative adjustment related to change in accounting principle	2,680,468			2,662,641			$ 265,821		$ 87,474	$ 791,465	1,577,195			$ (18,517)	$ (40,797)	$ 17,827
Balance (in shares) at Dec. 31, 2017							4,007,000		87,473,708
Balance at Dec. 31, 2017	2,680,584			2,662,757			$ 265,821		$ 87,474	791,465	1,577,311			(18,517)	(40,797)	17,827
Increase (Decrease) in Equity
Net income	227,472			218,706							218,706					8,766
Other comprehensive income (loss), net of tax	(46,742)			(46,742)										(46,742)		0
Net investment by (distribution to) non-controlling interest	(5,439)															(5,439)
Redemption of Series B Preferred Stock (in shares)								(4,000,000)
Redemption of Series B Preferred Stock		$ (100,000)			$ (100,000)			$ (96,519)				$ (3,481)
Repurchases of shares of common stock	(149,912)			(149,912)											(149,912)
Dividends on Preferred Stock		$ 0	$ (9,094)		$ 0	$ (9,094)						$ 0	$ (9,094)
Dividends on common stock	(74,916)			(74,916)							(74,916)
Common stock warrants exercised (in shares)									533,548
Common stock warrants exercised									$ 534	(534)
Common shares purchased by TCF employee benefit plans (in shares)									17,594
Common shares purchased by TCF employee benefit plans	715			715					$ 17	698
Stock compensation plans, net of tax (in shares)									176,195
Stock compensation plans, net of tax	5,460			5,460					$ 176	5,284
Change in shares held in trust for deferred compensation plans, at cost										(1,057)					1,057
Balance (in shares) at Sep. 30, 2018							7,000		88,201,045
Balance at Sep. 30, 2018	2,528,012			2,506,858			$ 169,302		$ 88,201	795,856	1,708,410			(65,259)	(189,652)	21,154
Balance (in shares) at Jun. 30, 2018							7,000		88,166,532
Balance at Jun. 30, 2018	2,504,579			2,480,933			$ 169,302		$ 88,167	790,933	1,649,449			(52,811)	(164,107)	23,646
Increase (Decrease) in Equity
Net income	88,839			86,196							86,196					2,643
Other comprehensive income (loss), net of tax	(12,448)			(12,448)							0			(12,448)		0
Net investment by (distribution to) non-controlling interest	(5,135)															(5,135)
Repurchases of shares of common stock	(24,026)			(24,026)											(24,026)
Dividends on Preferred Stock			(2,494)			(2,494)							(2,494)
Dividends on common stock	(24,741)			(24,741)							(24,741)
Common stock warrants exercised (in shares)									40,304
Common stock warrants exercised									$ 40	(40)
Stock compensation plans, net of tax (in shares)									(5,791)
Stock compensation plans, net of tax	3,438			3,438					$ (6)	3,444
Change in shares held in trust for deferred compensation plans, at cost										1,519					(1,519)
Balance (in shares) at Sep. 30, 2018							7,000		88,201,045
Balance at Sep. 30, 2018	2,528,012			2,506,858			$ 169,302		$ 88,201	795,856	1,708,410			(65,259)	(189,652)	21,154
Balance (in shares) at Dec. 31, 2018							7,000		88,198,460
Balance at Dec. 31, 2018	2,556,260			2,537,801			$ 169,302		$ 88,198	798,627	1,766,994			(33,138)	(252,182)	18,459
Increase (Decrease) in Equity
Net income	192,470			183,069							183,069			0	0	9,401
Other comprehensive income (loss), net of tax	89,366			89,366							0			89,366	0	0
Reverse merger with Chemical Financial Corporation (in shares)									65,539,678
Reverse merger with Chemical Financial Corporation	3,018,556			3,018,556					$ 65,540	2,687,153					265,863
Net investment by (distribution to) non-controlling interest	(4,547)															(4,547)
Repurchases of shares of common stock	(58,805)			(58,805)											(58,805)
Dividends on Preferred Stock			(7,481)			(7,481)							(7,481)
Dividends on common stock	(102,368)			(102,368)							(102,368)
Stock compensation plans, net of tax (in shares)									(166,757)
Stock compensation plans, net of tax	9,966			9,966					$ (167)	(5,626)					15,759
Change in shares held in trust for deferred compensation plans, at cost										(1,995)					1,995
Balance (in shares) at Sep. 30, 2019							7,000		153,571,381
Balance at Sep. 30, 2019	5,693,417			5,670,104			$ 169,302		$ 153,571	3,478,159	1,840,214			56,228	(27,370)	23,313
Balance (in shares) at Jun. 30, 2019							7,000		87,943,860
Balance at Jun. 30, 2019	2,710,517			2,685,659			$ 169,302		$ 87,944	781,788	1,874,308			37,334	(265,017)	24,858
Increase (Decrease) in Equity
Net income	24,978			22,148							22,148					2,830
Other comprehensive income (loss), net of tax	18,894			18,894							0			18,894		0
Reverse merger with Chemical Financial Corporation (in shares)									65,539,678
Reverse merger with Chemical Financial Corporation	3,018,556			3,018,556					$ 65,540	2,687,153					265,863
Net investment by (distribution to) non-controlling interest	(4,375)															(4,375)
Repurchases of shares of common stock	(32,310)			(32,310)											(32,310)
Dividends on Preferred Stock			$ (2,494)			$ (2,494)							$ (2,494)
Dividends on common stock	(53,748)			(53,748)							(53,748)
Stock compensation plans, net of tax (in shares)									87,843
Stock compensation plans, net of tax	13,399			13,399					$ 87	13,070					242
Change in shares held in trust for deferred compensation plans, at cost										(3,852)					3,852
Balance (in shares) at Sep. 30, 2019							7,000		153,571,381
Balance at Sep. 30, 2019	$ 5,693,417			$ 5,670,104			$ 169,302		$ 153,571	$ 3,478,159	$ 1,840,214			$ 56,228	$ (27,370)	$ 23,313