Fair Value Measurements - Other Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments measured at fair value	$ 6,001,171	$ 5,894,478
Other Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments measured at fair value	391,496	398,092
Other investments measured at NAV as practical expedient	562,495	635,940
Total other investments shown on balance sheets	$ 953,991	$ 1,034,032