Investment Information - Limited partnership interests (Details) - USD ($) $ in Thousands		Jun. 30, 2017	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss		$ 1,035,744	$ 891,774
Aggregate unfunded commitments		1,560,000
Equity method investments
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss	[1]	948,856	800,970
Aggregate unfunded commitments		961,000	776,600
Fair value option
Schedule of Equity Method Investments [Line Items]
Maximum Exposure to Loss	[2]	86,888	90,804
Aggregate unfunded commitments		$ 67,700	$ 16,700

[1] Aggregate unfunded commitments were $961.0 million at June 30, 2017, compared to $776.6 million at December 31, 2016.

[2] Aggregate unfunded commitments were $67.7 million at June 30, 2017, compared to $16.7 million at December 31, 2016.