Summary of Components of Net Periodic Pension Cost (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 230	$ 729	$ 655	$ 3,742
Interest cost	164	301	554	952
Expected return on assets	(553)	(742)	(1,778)	(2,370)
Prior service costs	110	158	328	509
Amortization of losses	5		5
Curtailment charges		2,887		2,887
Settlement charges	147	326	1,110	2,039
Net periodic pension cost	$ 103	$ 3,659	$ 874	$ 7,759