Disclosures About Offsetting Assets And Liabilities (Financial Liabilities And Derivative Liabilities That Are Subject To Offset) (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Offsetting [Abstract]
Gross amounts of recognized liabilities, Securities lending	[1]	$ (429,372)	$ (219,782)
Net amounts presented in the Statement of Financial Condition, Securities lending	[1]	(429,372)	(219,782)
Gross amounts not offset in the Statement of Financial Position, Financial instruments, Securities lending	[1]	117,209	78,474
Gross amounts not offset in the Statement of Financial Position, Collateral pledged, Securities lending	[1]	307,128	133,772
Securities lending, Net amount	[1]	(5,035)	(7,536)
Gross amounts of recognized liabilities, Securities purchased under agreements to resell	[2]	(346,202)	(233,704)
Net amounts presented in the Statement of Financial Condition, Securities purchased under agreements to resell	[2]	(346,202)	(233,704)
Gross amounts not offset in the Statement of Financial Position, Financial instruments, Securities purchased under agreements to resell	[2]	272,052	233,624
Gross amounts not offset in the Statement of Financial Position, Collateral pledged, Securities purchased under agreements to resell	[2]	74,150	80
Gross amounts of recognized liabilities		(775,574)	(453,486)
Net amounts presented in the Statement of Financial Condition		(775,574)	(453,486)
Gross amounts not offset in the Statement of Financial Position, Financial instruments		389,261	312,098
Gross amounts not offset in the Statement of Financial Condition, Collateral pledged		381,278	133,852
Net amount		$ (5,035)	$ (7,536)

[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 counter party. These securities are included on the consolidated statements of financial condition unless we default. Collateral pledged by our company to the counter party includes U.S. government agency securities, U.S. government securities, and corporate fixed income securities with market values of $360.9 million and $241.4 million at March 31, 2018 and December 31, 2017, respectively.