PENSION AND OTHER POST-RETIREMENT BENEFIT PLANS - COMPONENTS OF NET PERIODIC BENEFIT COST (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits
Amounts recognized in net periodic benefit cost
Service cost	$ 23,075	$ 28,300	$ 26,935
Interest cost	41,875	44,179	48,886
Expected return on plan assets	(58,820)	(68,830)	(74,080)
Amortization of prior service (credit) cost	(1,555)	(1,178)	(667)
Amortization of net loss (gain)	34,940	30,510	23,360
Curtailment credit	0	(688)	0
Settlement loss	22,657	23,067	0
Total net periodic benefit cost	62,172	55,360	24,434
Change in plan assets and benefit obligations recognized in AOCI, pre-tax
Actuarial net (gain) loss	(31,772)	(21,554)	99,136
Prior service (credit) cost	(41,517)	1,748	833
Total recognized in other comprehensive (income) loss, pre-tax	(73,289)	(19,806)	99,969
Net amounts recognized in periodic benefit cost and AOCI	(11,117)	35,554	124,403
Other Benefits
Amounts recognized in net periodic benefit cost
Service cost	299	542	706
Interest cost	9,731	10,187	11,696
Expected return on plan assets	0	0	0
Amortization of prior service (credit) cost	575	611	616
Amortization of net loss (gain)	(13)	(57)	(141)
Curtailment credit	0	204	0
Settlement loss	0	0	0
Total net periodic benefit cost	10,592	11,487	12,877
Change in plan assets and benefit obligations recognized in AOCI, pre-tax
Actuarial net (gain) loss	(3,047)	(26,270)	36,021
Prior service (credit) cost	(572)	(834)	(629)
Total recognized in other comprehensive (income) loss, pre-tax	(3,619)	(27,104)	35,392
Net amounts recognized in periodic benefit cost and AOCI	$ 6,973	$ (15,617)	$ 48,269