Condensed Statements of Comprehensive Income (Loss) (unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (27,828)	$ 56,076
Unrealized gain (loss) on short-term investment securities and cash and cash equivalents, net of deferred taxes of $54 and $39	(321)	130
Other Comprehensive Income (Loss), Securities, Available-For-Sale, Cash And Cash Equivalents, Unrealized Holding Gain (Loss) Arising During Period, After Tax	185	130
Interest rate derivative loss reclassified into earnings, net of taxes of $24 and $27	41	47
Other comprehensive income	226	177
Comprehensive income (loss)	$ (27,602)	$ 56,253