Financial Instruments Roll Forward (Details) - Financial Instruments and Restricted Cash - Not Designated as Hedging Instrument - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Foreign Currency Financial Liabilities and Related Restricted Cash [Roll Forward]
Balance, beginning of period	$ 21,311	$ 25,090
Settlement of short sales of corporate securities	(419)	0
Short sales of corporate securities	209	19,341
Net investment losses	284	1,492
Receipt of dividends, net of interest expense	0	88
Balance of financial instrument liabilities and related restricted cash, end of period	$ 21,385	$ 46,011