Disclosures About Offsetting Assets And Liabilities (Financial Liabilities That Are Subject To Offset) (Details) (Parenthetical) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Offsetting Liabilities [Line Items]
Fair value of securities pledged as collateral to counter party	[1]	$ 437,544	$ 169,572
U.S. Government Agency Securities And U.S. Government Securities And Corporate Fixed Income Securities [Member] | Fair Value Of Securities Pledged As Collateral [Member]
Offsetting Liabilities [Line Items]
Fair value of securities pledged as collateral to counter party		$ 495,000	$ 558,600

[1] 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 $495.0 million and $558.6 million at March 31, 2019 and December 31, 2018, respectively.