Component of net periodic benefit (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ (14,879)	$ (11,240)	$ (10,618)
Net periodic pension cost not yet recognized	$ (14,879)	$ (11,240)	$ (10,618)