Disclosures About Offsetting Assets And Liabilities (Financial Liabilities And Derivative Liabilities That Are Subject To Offset) (Details) - USD ($) $ in Thousands		Sep. 30, 2019	Dec. 31, 2018
Offsetting [Abstract]
Gross amounts of recognized liabilities, Securities lending	[1]	$ (516,941)	$ (392,163)
Net amounts presented in the Statement of Financial Condition, Securities lending	[1]	(516,941)	(392,163)
Gross amounts not offset in the Statement of Financial Position, Financial instruments, Securities lending	[1]	139,759	57,328
Gross amounts not offset in the Statement of Financial Position, Collateral pledged, Securities lending	[1]	377,182	325,110
Securities lending, Net amount	[1]		(9,725)
Gross amounts of recognized liabilities, Securities purchased under agreements to resell	[2]	(564,892)	(535,394)
Net amounts presented in the Statement of Financial Condition, Securities purchased under agreements to resell	[2]	(564,892)	(535,394)
Gross amounts not offset in the Statement of Financial Position, Financial instruments, Securities purchased under agreements to resell	[2]	27,766	365,822
Gross amounts not offset in the Statement of Financial Position, Collateral pledged, Securities purchased under agreements to resell	[2]	537,126	169,572
Gross amounts of recognized liabilities		(1,081,833)	(927,557)
Net amounts presented in the Statement of Financial Condition		(1,081,833)	(927,557)
Gross amounts not offset in the Statement of Financial Position, Financial instruments		167,525	423,150
Gross amounts not offset in the Statement of Financial Condition, Collateral pledged		$ 914,308	494,682
Net amount			$ (9,725)

[1] Securities lending transactions are included in payables to brokers, dealers, and clearing organizations on the consolidated statements of financial condition. See Note 3 in the notes to consolidated financial statements for additional information on payables to brokers, dealers, and clearing organizations.

[2] Collateral pledged includes the fair value of securities pledged by our company to the counterparty. These securities are included in the consolidated statements of financial condition unless we default. Collateral pledged by our company to the counterparty includes U.S. government agency securities, U.S. government securities, and corporate fixed income securities with market values of $586.9 million and $558.6 million at September 30, 2019 and December 31, 2018, respectively.