Loans Receivable and Allowance for Credit Losses (Summary of Loans Receivable by Portfolio Segment and Impairment Method) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 79,547	$ 86,046
Collectively evaluated for impairment	9,740,096	9,753,812
Total loans	9,819,643	9,839,858
Mortgage Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	49,783	48,783
Collectively evaluated for impairment	6,895,504	6,731,039
Total loans	6,945,287	6,779,822
Commercial Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	28,359	35,832
Collectively evaluated for impairment	2,482,349	2,531,638
Total loans	2,510,708	2,567,470
Consumer Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	1,405	1,431
Collectively evaluated for impairment	362,243	491,135
Total loans	$ 363,648	$ 492,566