Pension Plans and Other Postretirement Benefits - Changes in Fair Value of Plans Level 3 Assets (Detail) (Total Pension Benefits, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning balance					$ 563,303
Fair value of plan assets, Ending Balance	607,694	[1]	616,545	[1]	563,303
Unobservable Inputs (Level 3)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning balance	123,599	[1]	70,829
Total gains (losses) relating to assets sold during the period	(10,112)	[2]	994	[3]
Total unrealized gains (losses) included in earnings relating to assets still held at the reporting date	13,144	[2]	(4,511)	[3]
Purchases	50,506		76,643
Sales	(96,397)		(20,356)
Fair value of plan assets, Ending Balance	$ 80,740	[1]	$ 123,599	[1]

[1] See Note 18 “Pension Plans and Other Postretirement Benefits” for further information about fair value measurements of our pension and postretirement plan assets, including the reconciliations of the plans’ Level 3 assets.

[2] These (losses) gains are recognized in the consolidated balance sheets and are included as changes in plan assets in the tables above.

[3] These gains (losses) are recognized in the consolidated balance sheets and are included as changes in plan assets in the tables above.