Loan Servicing Rights - Summary of Loan Servicing Rights (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Servicing Asset at Fair Value, Amount [Roll Forward]
Balance, beginning of period	$ 56,313	$ 23	$ 25
Acquired in the TCF/Chemical Merger	0	59,567	0
New servicing assets created	17,209	4,969	7
Impairment (charge) recovery	(17,605)	(3,882)	0
Amortization	(17,614)	(4,364)	(9)
Balance, end of period	38,303	56,313	23
Valuation allowance, end of period	(21,488)	(3,882)	0
Loans serviced for others that have servicing rights capitalized, end of period	$ 6,203,199	$ 6,566,892	$ 0