Guarantor and Non-Guarantor Financial Information - Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
CONDENSED CONSOLIDATING STATEMENTS OF INCOME
Operating revenues	$ 487,847	$ 1,060,787
Operating costs and other	449,177	730,416
Operating income from continuing operations	38,670	330,371
Other income (expense), net	472	609
Interest expense	(4,524)	(590)
Income from continuing operations before income taxes	34,618	330,390
Income tax provision	18,720	126,767
Income from continuing operations	15,898	203,623
Income from discontinued operations before income taxes	104	(15)
Income (loss) from discontinued operations	104	(15)
NET INCOME	16,002	203,608
Eliminations
CONDENSED CONSOLIDATING STATEMENTS OF INCOME
Operating revenues	(17)	(16)
Operating costs and other	(401)	(1,032)
Operating income from continuing operations	384	1,016
Other income (expense), net	(384)	(1,016)
Equity in net income of subsidiaries	(9,352)	(212,077)
Income from continuing operations before income taxes	(9,352)	(212,077)
Income from continuing operations	(9,352)	(212,077)
NET INCOME	(9,352)	(212,077)
Guarantor/Parent | Reportable Legal Entities
CONDENSED CONSOLIDATING STATEMENTS OF INCOME
Operating costs and other	2,705	3,021
Operating income from continuing operations	(2,705)	(3,021)
Other income (expense), net	20	1
Interest expense	(62)	(7)
Equity in net income of subsidiaries	17,549	205,359
Income from continuing operations before income taxes	14,802	202,332
Income tax provision	(1,200)	(1,276)
Income from continuing operations	16,002	203,608
NET INCOME	16,002	203,608
Issuer Subsidiary | Reportable Legal Entities
CONDENSED CONSOLIDATING STATEMENTS OF INCOME
Operating revenues	405,537	952,109
Operating costs and other	356,751	629,038
Operating income from continuing operations	48,786	323,071
Other income (expense), net	656	921
Interest expense	(4,718)
Interest income (expense)		18
Equity in net income of subsidiaries	(8,197)	6,718
Income from continuing operations before income taxes	36,527	330,728
Income tax provision	19,227	126,122
Income from continuing operations	17,300	204,606
NET INCOME	17,300	204,606
Non-Guarantor Subsidiaries | Reportable Legal Entities
CONDENSED CONSOLIDATING STATEMENTS OF INCOME
Operating revenues	82,327	108,694
Operating costs and other	90,122	99,389
Operating income from continuing operations	(7,795)	9,305
Other income (expense), net	180	703
Interest expense	256	(601)
Income from continuing operations before income taxes	(7,359)	9,407
Income tax provision	693	1,921
Income from continuing operations	(8,052)	7,486
Income from discontinued operations before income taxes	104	(15)
Income (loss) from discontinued operations	104	(15)
NET INCOME	$ (7,948)	$ 7,471