Employee Benefit Plans (Combined Activity in Corporations Defined Benefit Pension Plans) (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]
Benefit obligation at beginning of year	$ 157,855	$ 145,246	$ 132,456
Interest cost	7,801	7,892	7,724
Actuarial (gain) loss	18,436	10,383	10,189
Benefits paid	(5,934)	(5,666)	(5,123)
Benefit obligation at end of year	178,158	157,855	145,246
Fair value of plan assets at beginning of year	137,253	141,050	128,044
Actual return on plan assets	13,931	(3,776)	17,580
Employer contributions	651	5,645	549
Benefits paid	(5,934)	(5,666)	(5,123)
Fair value of plan assets at end of year	145,901	137,253	141,050
Funded status of the plan at end of year and accrued benefit liability recognized	32,257	20,602	4,196
Accumulated benefit obligation at end of year	$ 178,158	$ 157,855	$ 145,246