Ownership Interests in and Advances to Partner Companies and Funds - Summarized Balance Sheets for Equity Method Investments (Details) - High Traction Stage [Member] $ in Thousands	Dec. 31, 2019 USD ($) partner_company	Dec. 31, 2018 USD ($) partner_company
Summarized Equity Method Investee Disclosures [Line Items]
Current assets	$ 91,968	$ 168,659
Non-current assets	26,231	24,432
Total assets	118,199	193,091
Current liabilities	80,783	88,988
Non-current liabilities	87,081	109,924
Shareholders’ equity	(49,665)	(5,821)
Total liabilities and shareholders’ equity	$ 118,199	$ 193,091
Number of equity method ownership interests | partner_company	13	19