Investment income and net realized and unrealized gains - Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Gain realized from termination fee paid by FNF	$ 50,000	$ 50,000
Net unrealized gain of equity investment		4,000
Realized gain of equity investment		2,500
Impairment expenses		14,700
Realized gains from sales of equity investments with no previously readily determinable fair value			$ 1,300
Net unrealized investment losses recognized on equity securities still held		$ (4,042)	$ 2,162	$ 0
Net realized gains from sale of securities investments				3,200
Net realized losses from change in fair value of contingent consideration liabilities				$ 800