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	$ 312,683	$ 344,463
Company's investment in separate accounts
Other Long-Term Investment [Line Items]
Other long-term investments	39,304	34,088
Private equity
Other Long-Term Investment [Line Items]
Other long-term investments	151,796	139,493
Hedge funds
Other Long-Term Investment [Line Items]
Other long-term investments	52,791	81,104
Real estate-related
Other Long-Term Investment [Line Items]
Other long-term investments	12,135	11,912
Total joint ventures and limited partnerships
Other Long-Term Investment [Line Items]
Other long-term investments	216,722	232,509
Derivatives
Other Long-Term Investment [Line Items]
Other long-term investments	$ 56,657	$ 77,866