Condensed Statements of Comprehensive Income (Loss) (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (144,428)	$ 114,501	$ (172,256)	$ 170,577
Unrealized gain on short-term investment securities and cash and cash equivalents, net of deferred taxes of $5, $29, $59 and $67	18	98	203	228
Interest rate derivative loss reclassified into earnings, net of taxes of $15, $19, $39 and $46	48	54	89	101
Other comprehensive income	66	152	292	329
Comprehensive income (loss)	$ (144,362)	$ 114,653	$ (171,964)	$ 170,906