Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018
Condensed Consolidated Statements of Comprehensive Income (Loss)
Net income (loss)	$ 60,891	$ 18,959	$ (11,879)	$ 500,106	$ 79,850	$ 488,227
Other comprehensive income (loss), net of income taxes:
Unrealized depreciation on securities, net of income taxes of ($3.4) million and ($3.6) million for the three and six months ended March 31, 2018, respectively			(7,568)			(8,169)
Minimum pension liability adjustments, net of income taxes of ($0.1) million and ($0.1) million for the three and six months ended March 31, 2019, respectively, and ($0.2) million and ($0.3) million for the three and six months ended March 31, 2018, respectively	224		308		449	648
Other comprehensive income (loss)	224	$ 225	(7,260)	$ (261)	449	(7,521)
Comprehensive income (loss)	$ 61,115		$ (19,139)		$ 80,299	$ 480,706