Guarantees and Collateral (Collateral and Restricted Assets) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Financial Instruments Owned and Pledged as Collateral [Line Items]
Restricted cash	$ 2,503	$ 5,635
Bonds Available-for-Sale		85,347
Investments in partnerships	8,431	8,779
Total Assets Pledged	10,934	99,761
Debt and derivatives | SAWHF
Financial Instruments Owned and Pledged as Collateral [Line Items]
Restricted cash	1,356	1,340
Investments in partnerships	8,431	8,779
Total Assets Pledged	$ 9,787	$ 10,119
Ownership interest (as a percent)	11.85%	11.85%
Debt and derivatives TRSs
Financial Instruments Owned and Pledged as Collateral [Line Items]
Restricted cash		$ 4,287
Bonds Available-for-Sale		85,347
Total Assets Pledged		89,634
Other
Financial Instruments Owned and Pledged as Collateral [Line Items]
Restricted cash	$ 1,147	8
Total Assets Pledged	$ 1,147	$ 8