Consolidated Statements of Comprehensive Income - Parenthetical (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Net unrealized gain (loss) on derivative instruments arising during the period, tax	$ 0	$ (3,168)
Reclassification adjustment for (gain) loss on derivative instruments included in net income, tax	204	(1,626)
Amortization of postretirement liability losses included in net periodic benefit cost, tax	168	319
Foreign currency translation adjustments arising during the period, tax	28	37
Net unrealized gain (loss) on available-for-sale investments arising during the period, tax	(19)	(24)
Reclassification adjustment for (gain) loss on available-for-sale investments included in net income, tax	$ 20	$ 19