Fair Value Measurements - Other Investments (Details) - Recurring - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total other investments shown on balance sheets	$ 5,919,720	$ 5,894,478
Other Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other investments measured at fair value	390,736	398,092
Other investments measured at NAV as practical expedient	545,422	635,940
Total other investments shown on balance sheets	$ 936,158	$ 1,034,032