Variable Interest Entities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Non-controlling interest	$ 108,466	$ 111,292
Equity interest attributable to third party investors in New Ocean
Variable Interest Entity [Line Items]
Total net assets	242,605	223,373
Non-controlling interest	134,139	112,081
New Ocean Capital Management Ltd | Equity interest attributable to third party investors in New Ocean
Variable Interest Entity [Line Items]
Non-controlling interest	$ 500	$ 1,000