Investments (Other Long-Term Investments) (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Other Long-Term Investment [Line Items]
Other long-term investments	$ 179,005	$ 551,931
Private equity
Other Long-Term Investment [Line Items]
Other long-term investments	29,817	30,513
Hedge funds
Other Long-Term Investment [Line Items]
Other long-term investments	103,094	98,554
Real estate-related
Other Long-Term Investment [Line Items]
Other long-term investments	46,083	109,043
Total joint ventures and limited partnerships
Other Long-Term Investment [Line Items]
Other long-term investments	178,994	238,110
Derivatives
Other Long-Term Investment [Line Items]
Other long-term investments	$ 11	$ 313,821