Investment in Securities (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ 19,200,000		$ 19,200,000		$ 24,900,000
Debt Securities, Available-for-sale, Purchased with Credit Deterioration, Allowance for Credit Loss at Acquisition Date					2,600,000
Available-for-sale securities Realizes Losses - Write offs	(300,000)	$ (2,500,000)	(1,500,000)	$ (16,300,000)
Catch-up premium amortization adjustment	(2,900,000)	300,000	10,000	(4,400,000)
Residential mortgage loans | Loans held-for-investment [Member]
Securities, Available-for-sale [Line Items]
Financing Receivable, Allowance for Credit Loss	$ 1,500,000		1,500,000		$ 2,200,000
Realized Losses, Write offs on loans		$ (51,000)	$ (33,000)	$ (500,000)