Change in Projected Benefit Obligation and Plan Assets (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]
Projected benefit obligation, beginning of year	$ 25,828	$ 29,197
Service cost	889	3,059	1,864
Interest cost	712	1,225	1,479
Actuarial loss	3,059	301
Benefits paid	(29)	(16)
Amendments		2,432
Curtailment charge		1,022
Settlement loss	(3,718)	(11,392)
Projected benefit obligation, end of year	26,741	25,828	29,197
Fair value of assets, beginning of year	60,953	70,189
Actual return on assets	3,543	2,697
Settlements	(3,718)	(11,392)
Benefits and expenses paid	(681)	(541)
Fair value of assets, end of year	60,097	60,953	70,189
Funded status at end of year	$ 33,356	$ 35,125
Ratio of plan assets to projected benefit obligation	225.00%	236.00%