Components of Net Periodic Pension Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Summary of Components of Net Periodic Benefit Cost and Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income [Line Items]
Service cost	$ 265	$ 286	$ 795	$ 858
Interest cost	1,132	1,165	3,396	3,495
Expected return on assets	(1,901)	(1,825)	(5,702)	(5,476)
Recognized actuarial loss	827	1,055	2,480	3,165
Net periodic pension cost	$ 323	$ 681	$ 969	$ 2,042