OTHER DEFERRED CHARGES (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Other deferred charges
Preliminary surveys and investigations	$ 113,283	$ 111,592
Advances to operating agents of jointly owned facilities	10,334	11,871
Interest rate swaps	14,202	12,140
Other	6,241	3,775
Total other deferred charges	144,060	139,378
Holcomb Station Project
Other deferred charges
Preliminary surveys and investigations	$ 92,700	$ 91,300