Components of Net Periodic Benefit Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,481	$ 2,785	$ 4,962	$ 5,569
Interest cost	4,891	4,468	9,782	8,936
Expected return on plan assets	(8,251)	(7,725)	(16,502)	(15,450)
Amortization of prior service cost	21	26	42	52
Recognized net actuarial losses	2,203	3,327	4,406	6,654
Settlement / curtailment loss	57	0	114	0
Net periodic benefit cost	1,402	2,881	2,804	5,761
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	156	172	312	344
Interest cost	299	263	598	525
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	(84)	(106)	(168)	(212)
Recognized net actuarial losses	83	138	166	276
Settlement / curtailment loss	0	0	0	0
Net periodic benefit cost	$ 454	$ 467	$ 908	$ 933