Investments (Other Long-Term Investments) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Other Long-Term Investment [Line Items]
Other long-term investments	$ 190,020	$ 551,931
Private equity
Other Long-Term Investment [Line Items]
Other long-term investments	30,178	30,513
Hedge funds
Other Long-Term Investment [Line Items]
Other long-term investments	104,849	98,554
Real estate-related
Other Long-Term Investment [Line Items]
Other long-term investments	47,009	109,043
Total joint ventures and limited partnerships
Other Long-Term Investment [Line Items]
Other long-term investments	182,036	238,110
Derivatives
Other Long-Term Investment [Line Items]
Other long-term investments	$ 7,984	$ 313,821