Subsequent Events (Details) - USD ($)			9 Months Ended
		Oct. 28, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Subsequent Event [Line Items]
Interest rate			6.125%		6.125%
Repurchase of shares	[1]		$ 0	$ 50,000,000
Subsequent event | MP Thrift
Subsequent Event [Line Items]
Repurchase of shares (in shares)		4,587,647
Repurchase of shares		$ 150,000,000
Share price (in dollars per share)		$ 32.70
Subsequent event | Subordinated Debt
Subsequent Event [Line Items]
Debt instrument, face amount		$ 150,000,000
Interest rate		4.125%

[1] Includes dividend reinvestment shares