Loans Receivable and Allowance for Credit Losses (Summary of Allowance for Loan Losses by Portfolio Segment and Impairment Classification) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 4,802	$ 8,974
Collectively evaluated for impairment	80,789	92,492
Total	85,591	101,466	$ 75,143	$ 55,525	$ 55,525
Mortgage Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	927	4,220
Collectively evaluated for impairment	53,271	64,087
Total	54,198	68,307	47,500		25,511
Commercial Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	3,832	4,715
Collectively evaluated for impairment	22,470	22,369
Total	26,302	27,084	22,841	28,263	28,263
Consumer Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	43	39
Collectively evaluated for impairment	5,048	6,036
Total	$ 5,091	$ 6,075	$ 4,802	$ 1,751	$ 1,751