Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2018

Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]

Financial assets and liabilities measured at fair value on a recurring basis were as follows (in thousands):



	Level 1		Level 2		Level 3
Assets as of September 30, 2018:
Short-term investments - debt securities	$	30,837	$	—	$	—
Short-term investments - equity securities	3,011		—		—
Investment at fair value - warrants (Note 5)	—		—		4,110
Investment at fair value - common stock (Note 5)⁽¹⁾	32,538		—		—
Total recurring fair value measurements	$	66,386	$	—	$	4,110
Assets as of December 31, 2017:
Investment at fair value (Note 5)⁽¹⁾	$	—	$	—	$	104,754

Liabilities as of September 30, 2018:
Profits interest units	$	—	$	—	$	1,422
Liabilities as of December 31, 2017:
Profits interest units	$	—	$	—	$	3,041

Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]

A reconciliation of the activity for fair value measurements categorized within Level 1 and Level 3 for the nine months ended September 30, 2018 is as follows (in thousands):



	Investment at Fair Value									Other Liabilities
	Common Stock			Warrants			Total			Profits Interest Units
Opening balance as of January 1, 2018	$	90,795		$	13,959		$	104,754		$	3,041
Total gains and losses included in earnings for the period⁽¹⁾
Non-cash stock compensation expense - Profits Interests	—			—			—			(1,619		)
Change in fair value of investment, net	(42,278		)	(9,849		)	(52,127		)	—
Realized loss on sale	(5,539		)	—			(5,539		)	—
Purchases, issues, sales and settlements	(10,440		)	—			(10,440		)	—
Transfers to Level 1	(32,538		)	—			(32,538		)	—
Total recurring fair value measurements⁽¹⁾	$	—		$	4,110		$	4,110		$	1,422

Marketable Securities [Table Text Block]

Short-term marketable securities for the periods presented were comprised of the following (in thousands):



			Gross Unrealized					Gross Realized
Security Type	Cost		Gains		Losses			Gains		Losses		Fair Value
September 30, 2018:
U.S. government fixed income securities (Maturity dates in 2018)	$	30,843	$	—	$	(6	)	$	—	$	—	$	30,837
Equity securities	2,930				—			81		—		3,011
	$	33,773	$	—	$	(6	)	$	81	$	—	$	33,848