CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Statement [Abstract]
General and administrative expense	$ 2,603	$ 5,148	$ 5,660	$ 10,738
Operating loss	(2,603)	(5,148)	(5,660)	(10,738)
Other income (loss), net	3,118	(2,452)	1,233	(3,887)
Interest income	763	666	1,636	1,465
Interest expense	(5,682)	(3,422)	(8,217)	(6,112)
Equity income (loss), net	40,497	(14,540)	68,764	(11,794)
Net income (loss) before income taxes	36,093	(24,896)	57,756	(31,066)
Income tax benefit (expense)	0	0	0	0
Net income (loss)	$ 36,093	$ (24,896)	$ 57,756	$ (31,066)
Net income (loss) per share:
Basic (in dollars per share)	$ 1.75	$ (1.21)	$ 2.80	$ (1.51)
Diluted (in dollars per share)	$ 1.75	$ (1.21)	$ 2.80	$ (1.51)
Weighted average shares used in computing income (loss) per share:
Basic (in shares)	20,628	20,539	20,606	20,523
Diluted (in shares)	20,658	20,539	20,606	20,523