EMPLOYEE BENEFIT PLANS - Plan assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Change in plan assets
Fair value of plan assets at beginning of year	$ 98,060	$ 108,157
Fair value of plan assets at end of year	$ 90,748	98,060	$ 108,157
DEFINED CONTRIBUTION PLAN
Percentage of employer's contribution under 401(k)/ Thrift Plan matching the first 5 percent of participant's compensation subject to certain limitations	100.00%
Percentage of participant's compensation eligible for employer's matching contribution	5.00%
Annual expense incurred for defined contribution plan	$ 21,600	24,800	32,300
General and Administrative
DEFINED CONTRIBUTION PLAN
Employer contribution	6,300
Oil and Gas Properties
Change in plan assets
Fair value of plan assets at beginning of year	387	301
Unrealized gains (losses) relating to property still held at the reporting date	(210)	86
Fair value of plan assets at end of year	$ 177	$ 387	$ 301