CONSOLIDATED STATEMENTS OF PATRONAGE CAPITAL AND MEMBERSHIP FEES AND ACCUMULATED OTHER COMPREHENSIVE MARGIN (DEFICIT) - USD ($) $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Increase (Decrease) in Members' Capital
Balance		$ 761,592		$ 713,940	$ 761,592	$ 713,940	$ 673,912
Components of comprehensive margin:
Net margin	$ 6,212	15,369	$ (4,237)	19,223	48,341	46,635	41,480
Unrealized gain (loss) on available-for-sale securities					(410)	1,017	(1,452)
Total comprehensive margin					47,931	47,652	40,028
Balance	809,523		761,592		809,523	761,592	713,940
Patronage Capital and Membership Fees
Increase (Decrease) in Members' Capital
Balance		761,124		714,489	761,124	714,489	673,009
Components of comprehensive margin:
Net margin					48,341	46,635	41,480
Balance	809,465		761,124		809,465	761,124	714,489
Accumulated Other Comprehensive Margin (Deficit)
Increase (Decrease) in Members' Capital
Balance		$ 468		$ (549)	468	(549)	903
Components of comprehensive margin:
Unrealized gain (loss) on available-for-sale securities					(410)	1,017	(1,452)
Balance	$ 58		$ 468		$ 58	$ 468	$ (549)