Investments (Schedule of Fair Value of Equity Investments Trading) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity investments trading	$ 388,424	$ 383,313
Financials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity investments trading	271,665	275,065
Communications and technology
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity investments trading	41,516	36,770
Industrial, utilities and energy
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity investments trading	30,976	30,303
Consumer
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity investments trading	21,461	20,501
Healthcare
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity investments trading	18,918	17,245
Basic materials
Schedule of Trading Securities and Other Trading Assets [Line Items]
Equity investments trading	$ 3,888	$ 3,429