Investments (Schedule of Fair Value of Equity Investments Trading) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity investments trading	$ 345,565	$ 393,877
Financials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity investments trading	238,572	193,716
Communications and technology
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity investments trading	36,421	65,833
Industrial, utilities and energy
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity investments trading	28,361	51,168
Consumer
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity investments trading	20,846	40,918
Healthcare
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity investments trading	17,966	36,148
Basic materials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity investments trading	$ 3,399	$ 6,094