PENSIONS AND OTHER POSTRETIREMENT BENEFITS - Schedules Related to RIGP and Retiree Medical Plan (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
AOCI:
Total	$ 7,093	$ 11,123
RIGP
Liabilities:
Accrued employee benefit liabilities - current	0	0
Accrued employee benefit liabilities - noncurrent	(11,861)	(11,245)
Total	(11,861)	(11,245)
AOCI:
Net actuarial loss	5,804	6,062
Total	5,804	6,062
Accumulated benefit obligation in excess of plan assets
Projected benefit obligation	17,405	17,988
Accumulated benefit obligation	13,357	13,602
Fair value of plan assets	$ 5,544	$ 6,743
Weighted average assumptions used in determining net periodic benefit cost for the Plans
Discount rate	3.30%	3.50%	2.70%
Expected return on plan assets	5.80%	5.80%	5.80%
Rate of compensation increase	3.00%	3.00%	3.00%
Assumptions used in determining benefit obligations for the Plans
Discount rate	3.50%	3.30%
Rate of compensation increase	3.00%	3.00%
Retiree Medical Plan
Liabilities:
Accrued employee benefit liabilities - current	$ (2,948)	$ (2,998)
Accrued employee benefit liabilities - noncurrent	(30,782)	(33,119)
Total	(33,730)	(36,117)
AOCI:
Net actuarial loss	1,289	5,061
Total	$ 1,289	$ 5,061
Weighted average assumptions used in determining net periodic benefit cost for the Plans
Discount rate	3.90%	4.40%	3.60%
Rate of compensation increase	3.00%	3.00%	3.00%
Assumptions used in determining benefit obligations for the Plans
Discount rate	4.10%	3.90%
Rate of compensation increase	3.00%	3.00%
Effect of 1% movement in assumed health care cost trend rates
Effect of 1% increase on total service cost and interest cost components	$ 56
Effect of 1% decrease on total service cost and interest cost components	(50)
Effect of 1% increase on postretirement benefit obligation	778
Effect of 1% decrease on postretirement benefit obligation	$ (700)