Consolidated Entities - ISP Fund LP (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
CONSOLIDATED ENTITIES
Total assets	$ 1,088,290		$ 999,570	[1]
Unrealized gain on equity investments	$ 54,673	$ 21,915
ISP Fund LP
CONSOLIDATED ENTITIES
Contributed to partnership for investing			$ 300,000
Economic interest of the Partnership (in percent)	100.00%
Total assets	$ 304,700
Net investment-related expense	400
Unrealized gain on equity investments	$ 5,800

[1] Consolidated balance sheet as of December 31, 2020 has been derived from audited consolidated financial statements.