Ownership Interests in and Advances to Partner Companies and Funds - Summarized Balance Sheets for Equity Method Investments (Details) $ in Thousands	Dec. 31, 2017 USD ($) partner_company	Dec. 31, 2016 USD ($) partner_company
High Traction Stage [Member]
Summarized Equity Method Investee Disclosures [Line Items]
Current assets	$ 251,986	$ 229,756
Non-current assets	111,329	106,555
Total assets	363,315	336,311
Current liabilities	296,349	215,622
Non-current liabilities	70,042	110,315
Shareholders’ equity	(3,076)	10,374
Total liabilities and shareholders’ equity	$ 363,315	$ 336,311
Number of partner companies | partner_company	3	5
Expansion Stage [Member]
Summarized Equity Method Investee Disclosures [Line Items]
Current assets	$ 75,441	$ 88,287
Non-current assets	20,833	18,874
Total assets	96,274	107,161
Current liabilities	75,610	48,522
Non-current liabilities	33,180	18,048
Shareholders’ equity	(12,516)	40,591
Total liabilities and shareholders’ equity	$ 96,274	$ 107,161
Number of partner companies | partner_company	11	11
Initial Revenue Stage [Member]
Summarized Equity Method Investee Disclosures [Line Items]
Current assets	$ 54,383	$ 51,615
Non-current assets	2,545	3,797
Total assets	56,928	55,412
Current liabilities	36,479	21,569
Non-current liabilities	17,450	30,188
Shareholders’ equity	2,999	3,655
Total liabilities and shareholders’ equity	$ 56,928	$ 55,412
Number of partner companies | partner_company	11	13