OTHER DEFERRED CHARGES (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Other deferred charges
Preliminary surveys and investigations	$ 20,135	$ 111,592
Advances to operating agents of jointly owned facilities	12,238	11,871
Interest rate swaps	9,056	12,140
Other	3,715	3,775
Total other deferred charges	45,144	139,378
Holcomb Expansion
Other deferred charges
Preliminary surveys and investigations	$ 0	$ 91,300