Other Investments - Components of other investments (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Other Investments [Line Items]
Other investments	$ 1,164,564	$ 1,433,057
Hedge funds
Other Investments [Line Items]
Other investments	331,972	544,070
Arbitrage
Other Investments [Line Items]
Other investments	165,053	205,117
Directional
Other Investments [Line Items]
Other investments	159,701	276,277
Event driven
Other Investments [Line Items]
Other investments	2,877	5,427
Multi-style
Other Investments [Line Items]
Other investments	4,341	57,249
Private investment funds
Other Investments [Line Items]
Other investments	175,579	244,576
Overseas deposits
Other Investments [Line Items]
Other investments	493,594	479,187
Structured transactions
Other Investments [Line Items]
Other investments	142,698	138,608
Other
Other Investments [Line Items]
Other investments	$ 20,721	$ 26,616