Investments (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Change In Equity Securities without Readily Determinable Fair Value, Impairment Loss, Cumulative Amount [Roll Forward]
Cost of investments, beginning of period	$ 44,136	$ 36,136
Cumulative downward adjustment/ impairment, beginning of period	(15,000)	0
Cumulative upward adjustment, beginning of period	1,200	0
Carrying amount, beginning of period	30,336	36,136
Cumulative upward adjustment, additions	1,150	0
Cost of investments, additions	0	0
Cumulative downward adjustment/impairment, additions	0	0
Carrying amount, additions	1,150	0
Cost of investments, end of period	44,136	36,136
Cumulative downward adjustment/ impairment, end of period	(15,000)	0
Cumulative upward adjustment, end of period	2,350	0
Carrying amount, end of period	31,486	36,136
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount	30,336	$ 36,136
Level III
Change In Equity Securities without Readily Determinable Fair Value, Impairment Loss, Cumulative Amount [Roll Forward]
Carrying amount, beginning of period	22,300
Carrying amount, end of period	26,500
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying amount	$ 22,300