EMPLOYEE BENEFIT PLANS - Periodic Benefit Cost and Other Changes (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other changes in plan assets and benefit obligations recognized in accumulated other comprehensive income:
Total recognized in accumulated other comprehensive income/(loss)		$ 1,290	$ (26,128)	$ 32,545
Pension Plan
Components of net periodic benefit cost:
Service cost		2,473	2,174	2,783
Interest cost		4,296	4,074	3,640
Expected return on plan assets		(5,590)	(5,475)	(4,446)
Amortization of net loss		3,354	773	2,653
Net periodic benefit cost		4,533	1,546	4,630
Other changes in plan assets and benefit obligations recognized in accumulated other comprehensive income:
Net actuarial loss		(863)	(23,821)	12,472
Reversal of amortization item: net actuarial (gain) loss	[1]	3,354	773	2,653
Total recognized in accumulated other comprehensive income/(loss)		2,491	(23,048)	15,125
Net periodic benefit cost		(4,533)	(1,546)	$ (4,630)
Total recognized in net periodic benefit cost and accumulated other comprehensive (loss) income		$ (2,042)	$ (24,594)

[1] Amortization of actuarial gain or loss is included in the computation of net periodic benefit cost (see Notes 14 and 18 for additional details).