Summary of Components of Net Periodic Benefit Cost and Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Defined benefit pension plans
Net periodic benefit cost:
Service cost	$ 7,515		$ 12,982		$ 13,285
Interest cost	27,708		25,580		29,530
Expected return on plan assets	(31,833)		(29,786)		(31,270)
Amortization of prior service credit	(1,037)		(1,057)		(502)
Recognized actuarial loss	15,771		21,193		19,020
Settlement loss			1,835		3,534
Net periodic benefit cost	18,124		30,747		33,597
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net actuarial loss (gain)	48,502		(95,744)		27,144
Prior service cost (credit)	20				(11,789)
Amortization of prior service credit	1,037		1,057		501
Total recognized in other comprehensive income	49,559	[1]	(94,687)	[1]	15,856	[1]
Total recognized in net periodic benefit cost and other comprehensive income	67,683		(63,940)		49,453
Postretirement benefit plans
Net periodic benefit cost:
Service cost	67		82		79
Interest cost	1,377		1,585		1,411
Recognized actuarial loss	17		578		117
Net periodic benefit cost	1,461		2,245		1,607
Other changes in plan assets and benefit obligations recognized in other comprehensive income:
Net actuarial loss (gain)	(2,205)		3,470		4,755
Total recognized in other comprehensive income	(2,205)	[1]	3,470	[1]	4,755	[1]
Total recognized in net periodic benefit cost and other comprehensive income	$ (744)		$ 5,715		$ 6,362

[1] Amounts exclude related tax (benefit) expense of $(17.8) million, $32.5 million, and $(2.3) million, during 2014, 2013, and 2012, respectively, which are also included in other comprehensive income.