Condensed Statements of Comprehensive Income (unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 114,501	$ 11,254	$ 170,577	$ (33,668)
Unrealized gain on short-term investment securities, net of deferred taxes of $29, $33, $67 and 26	98	101	228	78
Interest rate derivative loss reclassified into earnings, net of taxes of $19, $18, $46, and $39	54	61	101	120
Other comprehensive income	152	162	329	198
Comprehensive income (loss)	$ 114,653	$ 11,416	$ 170,906	$ (33,470)