CONSOLIDATED STATEMENTS OF PATRONAGE CAPITAL AND MEMBERSHIP FEES AND ACCUMULATED OTHER COMPREHENSIVE (DEFICIT) MARGIN - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Increase (Decrease) in Members' Capital
Beginning balance		$ 962,286		$ 911,087	$ 962,286	$ 911,087	$ 859,440
Net Margin	$ 3,196	23,596	$ (4,820)	27,400	54,461	51,199	51,277
Amounts reclassified to regulatory assets					0	0	370
Total comprehensive margin					54,461	51,199	51,647
Ending balance	1,016,747		962,286		1,016,747	962,286	911,087
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Beginning balance		962,286		911,087	962,286	911,087	859,810
Net Margin					54,461	51,199	51,277
Amounts reclassified to regulatory assets							0
Ending balance	1,016,747		962,286		1,016,747	962,286	911,087
Accumulated Other Comprehensive (Deficit) Margin
Increase (Decrease) in Members' Capital
Beginning balance		$ 0		$ 0	0	0	(370)
Net Margin					0	0	0
Amounts reclassified to regulatory assets							370
Ending balance	$ 0		$ 0		$ 0	$ 0	$ 0