Disclosures About Offsetting Assets and Liabilities (Financial Liabilities and Derivative Liabilities that are Subject to Offset) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Offsetting [Abstract]
Gross amounts of recognized liabilities, Securities lending	$ (183,564)	$ (145,124)
Net amounts presented in the Statement of Financial Condition, Securities lending	(183,564)	(145,124)
Gross amounts not offset in the Statement of Financial Position, Financial instruments, Securities lending	39,225	46,183
Gross amounts not offset in the Statement of Financial Position, Collateral pledged, Securities lending	144,334	98,925
Securities lending, Net amount	(5)	(16)
Gross amounts of recognized liabilities, Securities purchased under agreements to resell	(195,451)	(190,955)
Net amounts presented in the Statement of Financial Condition, Securities purchased under agreements to resell	(195,451)	(190,955)
Gross amounts not offset in the Statement of Financial Position, Financial instruments, Securities purchased under agreements to resell	10,655	17,992
Gross amounts not offset in the Statement of Financial Position, Collateral pledged, Securities purchased under agreements to resell	184,796	172,963
Gross amounts of recognized liabilities	(379,015)	(336,079)
Net amounts presented in the Statement of Financial Condition	(379,015)	(336,079)
Gross amounts not offset in the Statement of Financial Position, Financial instruments	49,880	64,175
Gross amounts not offset in the Statement of Financial Condition, Collateral pledged	329,130	271,888
Net amount	$ (5)	$ (16)