CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
OTHER COMPREHENSIVE INCOME (LOSS)
Prior service (cost) credit arising during the period, tax effect	$ (1,255)	$ 337	$ 0
Net (loss) gain arising during the period, tax effect	(35,347)	8,340	43,017
Amortization of net loss, tax effect	9,959	11,986	7,611
Amortization of transition obligation, tax effect	0	166	297
Amortization of prior service credit, tax effect	$ 1,709	$ 1,678	$ 8,063