Accumulated Other Comprehensive Loss - Summary of Income Tax Expense (Benefit) Associated with Various Components of Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Tax expense (benefit) associated with changes in:
Unrealized employee benefit costs	$ (2,429)	$ 0
Unrealized holding gains on marketable securities	(2)	(26)
Fair value of cash flow hedges	50	128
Tax expense (benefit) associated with reclassification adjustments:
Amortization of unrecognized employee benefit costs	(1,044)	(512)
Realized gains from sale of marketable securities	0	10
Realized gains/losses from settlement of cash flow hedges	$ (72)	$ (11)