Accounting Policies (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Accrued interest receivable	$ 48,091,000	$ 32,660,000
Allowance for credit losses, held-to-maturity portfolio	0
Allowance for credit losses, available-for-sale portfolio	0
Held-to-maturity debt securities
Marketable Securities [Line Items]
Accrued interest receivable	1,520,000
Available-for-sale debt securities
Marketable Securities [Line Items]
Accrued interest receivable	8,930,000
Loans receivable
Marketable Securities [Line Items]
Accrued interest receivable	$ 36,500,000