Derivatives (Offsetting Derivative Assets and Liabilities Subject to Master Netting Arrangements) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Gross Amounts Recognized, Derivative Assets	$ 60,231	$ 27,938
Gross Amounts Offset in the Statement of Financial Condition, Derivative Assets	(60,231)	(27,915)
Net Amounts Presented in the Statement of Financial Condition, Derivative Assets		23
Gross Amounts Not Offset in the Statement of Financial Condition - Financial Instruments, Derivative Assets		23
Gross Amounts Recognized, Derivative Liabilities	195,780	56,523
Gross Amounts Offset in the Statement of Financial Condition, Derivative Liabilities	(148,738)	(44,570)
Net Amounts Presented in the Statement of Financial Condition, Derivative Liabilities	47,042	11,953
Gross Amounts Not Offset in the Statement of Financial Condition - Financial Instruments, Derivative Liabilities		23
Gross Amounts Not offset in the Statement of Financial Condition - Cash Collateral, Derivative Liabilities	87,926	35,113
Net Amounts Presented in the Statement of Financial Condition, Derivative Liabilities	$ (40,884)	$ (23,183)