Investments (Other Long-term Investments) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Other long-term investments	$ 251,188	$ 551,931
Private Equity Funds
Debt Instrument [Line Items]
Other long-term investments	30,731	30,513
Hedge Funds
Debt Instrument [Line Items]
Other long-term investments	101,784	98,554
Real Estate Properties
Debt Instrument [Line Items]
Other long-term investments	45,519	109,043
Joint Ventures And Limited Partnerships
Debt Instrument [Line Items]
Other long-term investments	178,034	238,110
Derivatives
Debt Instrument [Line Items]
Other long-term investments	$ 73,154	$ 313,821